diff --git a/src/main/java/io/reactivex/rxjava3/core/Completable.java b/src/main/java/io/reactivex/rxjava3/core/Completable.java
index 9d785d96d5..3e8c84835f 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Completable.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Completable.java
@@ -151,7 +151,7 @@ public static Completable ambArray(@NonNull CompletableSource... sources) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static Completable amb(@NonNull Iterable<? extends CompletableSource> sources) {
+    public static Completable amb(@NonNull Iterable<@NonNull ? extends CompletableSource> sources) {
         Objects.requireNonNull(sources, "sources is null");
 
         return RxJavaPlugins.onAssembly(new CompletableAmb(null, sources));
@@ -216,7 +216,7 @@ public static Completable concatArray(@NonNull CompletableSource... sources) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static Completable concat(@NonNull Iterable<? extends CompletableSource> sources) {
+    public static Completable concat(@NonNull Iterable<@NonNull ? extends CompletableSource> sources) {
         Objects.requireNonNull(sources, "sources is null");
 
         return RxJavaPlugins.onAssembly(new CompletableConcatIterable(sources));
@@ -241,7 +241,7 @@ public static Completable concat(@NonNull Iterable<? extends CompletableSource>
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static Completable concat(@NonNull Publisher<? extends CompletableSource> sources) {
+    public static Completable concat(@NonNull Publisher<@NonNull ? extends CompletableSource> sources) {
         return concat(sources, 2);
     }
 
@@ -266,7 +266,7 @@ public static Completable concat(@NonNull Publisher<? extends CompletableSource>
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    public static Completable concat(@NonNull Publisher<? extends CompletableSource> sources, int prefetch) {
+    public static Completable concat(@NonNull Publisher<@NonNull ? extends CompletableSource> sources, int prefetch) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new CompletableConcat(sources, prefetch));
@@ -733,7 +733,7 @@ public static Completable mergeArray(@NonNull CompletableSource... sources) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static Completable merge(@NonNull Iterable<? extends CompletableSource> sources) {
+    public static Completable merge(@NonNull Iterable<@NonNull ? extends CompletableSource> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new CompletableMergeIterable(sources));
     }
@@ -772,7 +772,7 @@ public static Completable merge(@NonNull Iterable<? extends CompletableSource> s
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @NonNull
-    public static Completable merge(@NonNull Publisher<? extends CompletableSource> sources) {
+    public static Completable merge(@NonNull Publisher<@NonNull ? extends CompletableSource> sources) {
         return merge0(sources, Integer.MAX_VALUE, false);
     }
 
@@ -813,7 +813,7 @@ public static Completable merge(@NonNull Publisher<? extends CompletableSource>
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static Completable merge(@NonNull Publisher<? extends CompletableSource> sources, int maxConcurrency) {
+    public static Completable merge(@NonNull Publisher<@NonNull ? extends CompletableSource> sources, int maxConcurrency) {
         return merge0(sources, maxConcurrency, false);
     }
 
@@ -840,7 +840,7 @@ public static Completable merge(@NonNull Publisher<? extends CompletableSource>
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    private static Completable merge0(@NonNull Publisher<? extends CompletableSource> sources, int maxConcurrency, boolean delayErrors) {
+    private static Completable merge0(@NonNull Publisher<@NonNull ? extends CompletableSource> sources, int maxConcurrency, boolean delayErrors) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new CompletableMerge(sources, maxConcurrency, delayErrors));
@@ -886,7 +886,7 @@ public static Completable mergeArrayDelayError(@NonNull CompletableSource... sou
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static Completable mergeDelayError(@NonNull Iterable<? extends CompletableSource> sources) {
+    public static Completable mergeDelayError(@NonNull Iterable<@NonNull ? extends CompletableSource> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new CompletableMergeDelayErrorIterable(sources));
     }
@@ -912,7 +912,7 @@ public static Completable mergeDelayError(@NonNull Iterable<? extends Completabl
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @NonNull
-    public static Completable mergeDelayError(@NonNull Publisher<? extends CompletableSource> sources) {
+    public static Completable mergeDelayError(@NonNull Publisher<@NonNull ? extends CompletableSource> sources) {
         return merge0(sources, Integer.MAX_VALUE, true);
     }
 
@@ -940,7 +940,7 @@ public static Completable mergeDelayError(@NonNull Publisher<? extends Completab
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static Completable mergeDelayError(@NonNull Publisher<? extends CompletableSource> sources, int maxConcurrency) {
+    public static Completable mergeDelayError(@NonNull Publisher<@NonNull ? extends CompletableSource> sources, int maxConcurrency) {
         return merge0(sources, maxConcurrency, true);
     }
 
@@ -1582,7 +1582,7 @@ public final Completable doOnError(@NonNull Consumer<? super Throwable> onError)
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Completable doOnEvent(@NonNull Consumer<? super Throwable> onEvent) {
+    public final Completable doOnEvent(@NonNull Consumer<@Nullable ? super Throwable> onEvent) {
         Objects.requireNonNull(onEvent, "onEvent is null");
         return RxJavaPlugins.onAssembly(new CompletableDoOnEvent(this, onEvent));
     }
@@ -2083,7 +2083,7 @@ public final Completable repeatUntil(@NonNull BooleanSupplier stop) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Completable repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<?>> handler) {
+    public final Completable repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<@NonNull ?>> handler) {
         return fromPublisher(toFlowable().repeatWhen(handler));
     }
 
@@ -2234,7 +2234,7 @@ public final Completable retry(@NonNull Predicate<? super Throwable> predicate)
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Completable retryWhen(@NonNull Function<? super Flowable<Throwable>, ? extends Publisher<?>> handler) {
+    public final Completable retryWhen(@NonNull Function<? super Flowable<Throwable>, ? extends Publisher<@NonNull ?>> handler) {
         return fromPublisher(toFlowable().retryWhen(handler));
     }
 
diff --git a/src/main/java/io/reactivex/rxjava3/core/CompletableConverter.java b/src/main/java/io/reactivex/rxjava3/core/CompletableConverter.java
index bcc00f088b..83e8f693eb 100644
--- a/src/main/java/io/reactivex/rxjava3/core/CompletableConverter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/CompletableConverter.java
@@ -23,13 +23,12 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface CompletableConverter<R> {
+public interface CompletableConverter<@NonNull R> {
     /**
      * Applies a function to the upstream Completable and returns a converted value of type {@code R}.
      *
      * @param upstream the upstream Completable instance
      * @return the converted value
      */
-    @NonNull
     R apply(@NonNull Completable upstream);
 }
diff --git a/src/main/java/io/reactivex/rxjava3/core/Emitter.java b/src/main/java/io/reactivex/rxjava3/core/Emitter.java
index 0fc2b47c0d..e9ea2a1827 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Emitter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Emitter.java
@@ -25,7 +25,7 @@
  *
  * @param <T> the value type emitted
  */
-public interface Emitter<T> {
+public interface Emitter<@NonNull T> {
 
     /**
      * Signal a normal value.
diff --git a/src/main/java/io/reactivex/rxjava3/core/Flowable.java b/src/main/java/io/reactivex/rxjava3/core/Flowable.java
index 56fa2e63f2..486b0cb629 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Flowable.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Flowable.java
@@ -150,7 +150,7 @@
  * @see ParallelFlowable
  * @see io.reactivex.rxjava3.subscribers.DisposableSubscriber
  */
-public abstract class Flowable<T> implements Publisher<T> {
+public abstract class Flowable<@NonNull T> implements Publisher<T> {
     /** The default buffer size. */
     static final int BUFFER_SIZE;
     static {
@@ -183,7 +183,7 @@ public abstract class Flowable<T> implements Publisher<T> {
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> amb(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> amb(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new FlowableAmb<>(null, sources));
     }
@@ -215,7 +215,7 @@ public static <T> Flowable<T> amb(@NonNull Iterable<? extends Publisher<? extend
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
-    public static <T> Flowable<T> ambArray(Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> ambArray(Publisher<@NonNull ? extends T>... sources) {
         Objects.requireNonNull(sources, "sources is null");
         int len = sources.length;
         if (len == 0) {
@@ -280,7 +280,7 @@ public static int bufferSize() {
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static <T, @NonNull R> Flowable<R> combineLatestArray(@NonNull Publisher<? extends T>[] sources, @NonNull Function<? super Object[], ? extends R> combiner) {
+    public static <T, @NonNull R> Flowable<R> combineLatestArray(@NonNull Publisher<@NonNull ? extends T>[] sources, @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatestArray(sources, combiner, bufferSize());
     }
 
@@ -329,7 +329,7 @@ public static int bufferSize() {
     @CheckReturnValue
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <T, R> Flowable<R> combineLatestArray(@NonNull Publisher<? extends T>[] sources, @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
+    public static <T, R> Flowable<R> combineLatestArray(@NonNull Publisher<@NonNull ? extends T>[] sources, @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         if (sources.length == 0) {
             return empty();
@@ -381,7 +381,7 @@ public static <T, R> Flowable<R> combineLatestArray(@NonNull Publisher<? extends
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static <T, @NonNull R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publisher<? extends T>> sources,
+    public static <T, @NonNull R> Flowable<R> combineLatest(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatest(sources, combiner, bufferSize());
     }
@@ -431,7 +431,7 @@ public static <T, R> Flowable<R> combineLatestArray(@NonNull Publisher<? extends
     @CheckReturnValue
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publisher<? extends T>> sources,
+    public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -481,7 +481,7 @@ public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publi
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static <T, @NonNull R> Flowable<R> combineLatestArrayDelayError(@NonNull Publisher<? extends T>[] sources,
+    public static <T, @NonNull R> Flowable<R> combineLatestArrayDelayError(@NonNull Publisher<@NonNull ? extends T>[] sources,
             @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatestArrayDelayError(sources, combiner, bufferSize());
     }
@@ -532,7 +532,7 @@ public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publi
     @CheckReturnValue
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <T, @NonNull R> Flowable<R> combineLatestArrayDelayError(@NonNull Publisher<? extends T>[] sources,
+    public static <T, @NonNull R> Flowable<R> combineLatestArrayDelayError(@NonNull Publisher<@NonNull ? extends T>[] sources,
             @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -586,7 +586,7 @@ public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publi
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static <T, @NonNull R> Flowable<R> combineLatestDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources,
+    public static <T, @NonNull R> Flowable<R> combineLatestDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatestDelayError(sources, combiner, bufferSize());
     }
@@ -637,7 +637,7 @@ public static <T, R> Flowable<R> combineLatest(@NonNull Iterable<? extends Publi
     @CheckReturnValue
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public static <T, R> Flowable<R> combineLatestDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources,
+    public static <T, R> Flowable<R> combineLatestDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -684,7 +684,7 @@ public static <T, R> Flowable<R> combineLatestDelayError(@NonNull Iterable<? ext
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
     public static <T1, T2, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
             @NonNull BiFunction<? super T1, ? super T2, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -734,8 +734,8 @@ public static <T1, T2, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3,
             @NonNull Function3<? super T1, ? super T2, ? super T3, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -790,8 +790,8 @@ public static <T1, T2, T3, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
             @NonNull Function4<? super T1, ? super T2, ? super T3, ? super T4, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -850,9 +850,9 @@ public static <T1, T2, T3, T4, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
-            @NonNull Publisher<? extends T5> source5,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T5> source5,
             @NonNull Function5<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -915,9 +915,9 @@ public static <T1, T2, T3, T4, T5, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
-            @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
             @NonNull Function6<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -985,10 +985,10 @@ public static <T1, T2, T3, T4, T5, T6, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
-            @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7,
             @NonNull Function7<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -1060,10 +1060,10 @@ public static <T1, T2, T3, T4, T5, T6, T7, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
-            @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7, @NonNull Publisher<? extends T8> source8,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7, @NonNull Publisher<@NonNull ? extends T8> source8,
             @NonNull Function8<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -1140,11 +1140,11 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Flowable<R> combineLatest(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Flowable<R> combineLatest(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
-            @NonNull Publisher<? extends T3> source3, @NonNull Publisher<? extends T4> source4,
-            @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7, @NonNull Publisher<? extends T8> source8,
-            @NonNull Publisher<? extends T9> source9,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T3> source3, @NonNull Publisher<@NonNull ? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7, @NonNull Publisher<@NonNull ? extends T8> source8,
+            @NonNull Publisher<@NonNull ? extends T9> source9,
             @NonNull Function9<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? super T9, ? extends R> combiner) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -1183,7 +1183,7 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Flowable<R> combineLatest(
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concat(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         // unlike general sources, fromIterable can only throw on a boundary because it is consumed only there
         return fromIterable(sources).concatMapDelayError((Function)Functions.identity(), false, 2);
@@ -1216,7 +1216,7 @@ public static <T> Flowable<T> concat(@NonNull Iterable<? extends Publisher<? ext
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return concat(sources, bufferSize());
     }
 
@@ -1251,7 +1251,7 @@ public static <T> Flowable<T> concat(@NonNull Publisher<? extends Publisher<? ex
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends Publisher<? extends T>> sources, int prefetch) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int prefetch) {
         return fromPublisher(sources).concatMap((Function)Functions.identity(), prefetch);
     }
 
@@ -1284,7 +1284,7 @@ public static <T> Flowable<T> concat(@NonNull Publisher<? extends Publisher<? ex
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         return concatArray(source1, source2);
@@ -1322,8 +1322,8 @@ public static <T> Flowable<T> concat(@NonNull Publisher<? extends T> source1, @N
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> concat(
-            @NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
-            @NonNull Publisher<? extends T> source3) {
+            @NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
+            @NonNull Publisher<@NonNull ? extends T> source3) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -1364,8 +1364,8 @@ public static <T> Flowable<T> concat(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> concat(
-            @NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
-            @NonNull Publisher<? extends T> source3, @NonNull Publisher<? extends T> source4) {
+            @NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
+            @NonNull Publisher<@NonNull ? extends T> source3, @NonNull Publisher<@NonNull ? extends T> source4) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -1398,7 +1398,7 @@ public static <T> Flowable<T> concat(
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> concatArray(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArray(@NonNull Publisher<@NonNull ? extends T>... sources) {
         Objects.requireNonNull(sources, "sources is null");
         if (sources.length == 0) {
             return empty();
@@ -1433,7 +1433,7 @@ public static <T> Flowable<T> concatArray(@NonNull Publisher<? extends T>... sou
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> concatArrayDelayError(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArrayDelayError(@NonNull Publisher<@NonNull ? extends T>... sources) {
         Objects.requireNonNull(sources, "sources is null");
         if (sources.length == 0) {
             return empty();
@@ -1472,7 +1472,7 @@ public static <T> Flowable<T> concatArrayDelayError(@NonNull Publisher<? extends
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> concatArrayEager(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArrayEager(@NonNull Publisher<@NonNull ? extends T>... sources) {
         return concatArrayEager(bufferSize(), bufferSize(), sources);
     }
 
@@ -1509,7 +1509,7 @@ public static <T> Flowable<T> concatArrayEager(@NonNull Publisher<? extends T>..
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
     @SafeVarargs
-    public static <T> Flowable<T> concatArrayEager(int maxConcurrency, int prefetch, @NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArrayEager(int maxConcurrency, int prefetch, @NonNull Publisher<@NonNull ? extends T>... sources) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -1545,7 +1545,7 @@ public static <T> Flowable<T> concatArrayEager(int maxConcurrency, int prefetch,
     @BackpressureSupport(BackpressureKind.FULL)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> concatArrayEagerDelayError(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArrayEagerDelayError(@NonNull Publisher<@NonNull ? extends T>... sources) {
         return concatArrayEagerDelayError(bufferSize(), bufferSize(), sources);
     }
 
@@ -1583,7 +1583,7 @@ public static <T> Flowable<T> concatArrayEagerDelayError(@NonNull Publisher<? ex
     @BackpressureSupport(BackpressureKind.FULL)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> concatArrayEagerDelayError(int maxConcurrency, int prefetch, @NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> concatArrayEagerDelayError(int maxConcurrency, int prefetch, @NonNull Publisher<@NonNull ? extends T>... sources) {
         return fromArray(sources).concatMapEagerDelayError((Function)Functions.identity(), true, maxConcurrency, prefetch);
     }
 
@@ -1611,7 +1611,7 @@ public static <T> Flowable<T> concatArrayEagerDelayError(int maxConcurrency, int
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concatDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concatDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return fromIterable(sources).concatMapDelayError((Function)Functions.identity());
     }
@@ -1636,7 +1636,7 @@ public static <T> Flowable<T> concatDelayError(@NonNull Iterable<? extends Publi
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return concatDelayError(sources, bufferSize(), true);
     }
 
@@ -1665,7 +1665,7 @@ public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources, int prefetch, boolean tillTheEnd) {
+    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int prefetch, boolean tillTheEnd) {
         return fromPublisher(sources).concatMapDelayError((Function)Functions.identity(), tillTheEnd, prefetch);
     }
 
@@ -1693,7 +1693,7 @@ public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return concatEager(sources, bufferSize(), bufferSize());
     }
 
@@ -1726,7 +1726,7 @@ public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends Publisher
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
-    public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends Publisher<? extends T>> sources, int maxConcurrency, int prefetch) {
+    public static <T> Flowable<T> concatEager(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency, int prefetch) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -1757,7 +1757,7 @@ public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends Publisher
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return concatEager(sources, bufferSize(), bufferSize());
     }
 
@@ -1790,7 +1790,7 @@ public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends Publisher<
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "rawtypes", "unchecked" })
-    public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency, int prefetch) {
+    public static <T> Flowable<T> concatEager(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency, int prefetch) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -1893,7 +1893,7 @@ public static <T> Flowable<T> create(@NonNull FlowableOnSubscribe<T> source, @No
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> defer(@NonNull Supplier<? extends Publisher<? extends T>> supplier) {
+    public static <T> Flowable<T> defer(@NonNull Supplier<? extends Publisher<@NonNull ? extends T>> supplier) {
         Objects.requireNonNull(supplier, "supplier is null");
         return RxJavaPlugins.onAssembly(new FlowableDefer<>(supplier));
     }
@@ -2178,7 +2178,7 @@ public static <T> Flowable<T> error(@NonNull Throwable throwable) {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <@NonNull T> Flowable<T> fromIterable(@NonNull Iterable<? extends T> source) {
+    public static <@NonNull T> Flowable<T> fromIterable(@NonNull Iterable<@NonNull ? extends T> source) {
         Objects.requireNonNull(source, "source is null");
         return RxJavaPlugins.onAssembly(new FlowableFromIterable<>(source));
     }
@@ -2215,7 +2215,7 @@ public static <T> Flowable<T> error(@NonNull Throwable throwable) {
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings("unchecked")
-    public static <T> Flowable<T> fromPublisher(@NonNull Publisher<? extends T> source) {
+    public static <T> Flowable<T> fromPublisher(@NonNull Publisher<@NonNull ? extends T> source) {
         if (source instanceof Flowable) {
             return RxJavaPlugins.onAssembly((Flowable<T>)source);
         }
@@ -2327,7 +2327,7 @@ public static <T> Flowable<T> generate(@NonNull Consumer<@NonNull Emitter<T>> ge
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, S> Flowable<T> generate(@NonNull Supplier<S> initialState, @NonNull BiConsumer<S, @NonNull Emitter<T>> generator) {
+    public static <T, S> Flowable<T> generate(@NonNull Supplier<S> initialState, @NonNull BiConsumer<S, Emitter<T>> generator) {
         Objects.requireNonNull(generator, "generator is null");
         return generate(initialState, FlowableInternalHelper.simpleBiGenerator(generator),
                 Functions.emptyConsumer());
@@ -2363,7 +2363,7 @@ public static <T, S> Flowable<T> generate(@NonNull Supplier<S> initialState, @No
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, S> Flowable<T> generate(@NonNull Supplier<S> initialState, @NonNull BiConsumer<S, @NonNull Emitter<T>> generator,
+    public static <T, S> Flowable<T> generate(@NonNull Supplier<S> initialState, @NonNull BiConsumer<S, Emitter<T>> generator,
             @NonNull Consumer<? super S> disposeState) {
         Objects.requireNonNull(generator, "generator is null");
         return generate(initialState, FlowableInternalHelper.simpleBiGenerator(generator), disposeState);
@@ -3142,7 +3142,7 @@ public static Flowable<Long> intervalRange(long start, long count, long initialD
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency, int bufferSize) {
+    public static <T> Flowable<T> merge(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency, int bufferSize) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), false, maxConcurrency, bufferSize);
     }
 
@@ -3196,7 +3196,7 @@ public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? exte
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> mergeArray(int maxConcurrency, int bufferSize, @NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> mergeArray(int maxConcurrency, int bufferSize, @NonNull Publisher<@NonNull ? extends T>... sources) {
         return fromArray(sources).flatMap((Function)Functions.identity(), false, maxConcurrency, bufferSize);
     }
 
@@ -3242,7 +3242,7 @@ public static <T> Flowable<T> mergeArray(int maxConcurrency, int bufferSize, @No
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return fromIterable(sources).flatMap((Function)Functions.identity());
     }
 
@@ -3293,7 +3293,7 @@ public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? exte
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> merge(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), maxConcurrency);
     }
 
@@ -3340,7 +3340,7 @@ public static <T> Flowable<T> merge(@NonNull Iterable<? extends Publisher<? exte
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return merge(sources, bufferSize());
     }
 
@@ -3393,7 +3393,7 @@ public static <T> Flowable<T> merge(@NonNull Publisher<? extends Publisher<? ext
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends Publisher<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency) {
         return fromPublisher(sources).flatMap((Function)Functions.identity(), maxConcurrency);
     }
 
@@ -3439,7 +3439,7 @@ public static <T> Flowable<T> merge(@NonNull Publisher<? extends Publisher<? ext
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> mergeArray(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> mergeArray(@NonNull Publisher<@NonNull ? extends T>... sources) {
         return fromArray(sources).flatMap((Function)Functions.identity(), sources.length);
     }
 
@@ -3486,7 +3486,7 @@ public static <T> Flowable<T> mergeArray(@NonNull Publisher<? extends T>... sour
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         return fromArray(source1, source2).flatMap((Function)Functions.identity(), false, 2);
@@ -3537,7 +3537,7 @@ public static <T> Flowable<T> merge(@NonNull Publisher<? extends T> source1, @No
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2, @NonNull Publisher<? extends T> source3) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2, @NonNull Publisher<@NonNull ? extends T> source3) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -3592,8 +3592,8 @@ public static <T> Flowable<T> merge(@NonNull Publisher<? extends T> source1, @No
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> merge(
-            @NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
-            @NonNull Publisher<? extends T> source3, @NonNull Publisher<? extends T> source4) {
+            @NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
+            @NonNull Publisher<@NonNull ? extends T> source3, @NonNull Publisher<@NonNull ? extends T> source4) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -3635,7 +3635,7 @@ public static <T> Flowable<T> merge(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true);
     }
 
@@ -3678,7 +3678,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publis
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency, int bufferSize) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency, int bufferSize) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true, maxConcurrency, bufferSize);
     }
 
@@ -3722,7 +3722,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publis
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> mergeArrayDelayError(int maxConcurrency, int bufferSize, @NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> mergeArrayDelayError(int maxConcurrency, int bufferSize, @NonNull Publisher<@NonNull ? extends T>... sources) {
         return fromArray(sources).flatMap((Function)Functions.identity(), true, maxConcurrency, bufferSize);
     }
 
@@ -3763,7 +3763,7 @@ public static <T> Flowable<T> mergeArrayDelayError(int maxConcurrency, int buffe
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publisher<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true, maxConcurrency);
     }
 
@@ -3801,7 +3801,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Publis
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return mergeDelayError(sources, bufferSize());
     }
 
@@ -3844,7 +3844,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends Publi
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int maxConcurrency) {
         return fromPublisher(sources).flatMap((Function)Functions.identity(), true, maxConcurrency);
     }
 
@@ -3883,7 +3883,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends Publi
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     @NonNull
-    public static <T> Flowable<T> mergeArrayDelayError(@NonNull Publisher<? extends T>... sources) {
+    public static <T> Flowable<T> mergeArrayDelayError(@NonNull Publisher<@NonNull ? extends T>... sources) {
         return fromArray(sources).flatMap((Function)Functions.identity(), true, sources.length);
     }
 
@@ -3922,7 +3922,7 @@ public static <T> Flowable<T> mergeArrayDelayError(@NonNull Publisher<? extends
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         return fromArray(source1, source2).flatMap((Function)Functions.identity(), true, 2);
@@ -3966,7 +3966,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends T> so
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2, @NonNull Publisher<? extends T> source3) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2, @NonNull Publisher<@NonNull ? extends T> source3) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -4014,8 +4014,8 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends T> so
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T> Flowable<T> mergeDelayError(
-            @NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
-            @NonNull Publisher<? extends T> source3, @NonNull Publisher<? extends T> source4) {
+            @NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
+            @NonNull Publisher<@NonNull ? extends T> source3, @NonNull Publisher<@NonNull ? extends T> source4) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
         Objects.requireNonNull(source3, "source3 is null");
@@ -4164,7 +4164,7 @@ public static Flowable<Long> rangeLong(long start, long count) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2) {
+    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2) {
         return sequenceEqual(source1, source2, ObjectHelper.equalsPredicate(), bufferSize());
     }
 
@@ -4199,7 +4199,7 @@ public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T>
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
+    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
             @NonNull BiPredicate<? super T, ? super T> isEqual) {
         return sequenceEqual(source1, source2, isEqual, bufferSize());
     }
@@ -4238,7 +4238,7 @@ public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T>
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2,
+    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2,
             @NonNull BiPredicate<? super T, ? super T> isEqual, int bufferSize) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -4277,7 +4277,7 @@ public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T>
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T> source1, @NonNull Publisher<? extends T> source2, int bufferSize) {
+    public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<@NonNull ? extends T> source1, @NonNull Publisher<@NonNull ? extends T> source2, int bufferSize) {
         return sequenceEqual(source1, source2, ObjectHelper.equalsPredicate(), bufferSize);
     }
 
@@ -4320,7 +4320,7 @@ public static <T> Single<Boolean> sequenceEqual(@NonNull Publisher<? extends T>
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> switchOnNext(@NonNull Publisher<? extends Publisher<? extends T>> sources, int bufferSize) {
+    public static <T> Flowable<T> switchOnNext(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int bufferSize) {
         return fromPublisher(sources).switchMap((Function)Functions.identity(), bufferSize);
     }
 
@@ -4360,7 +4360,7 @@ public static <T> Flowable<T> switchOnNext(@NonNull Publisher<? extends Publishe
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> switchOnNext(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> switchOnNext(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return fromPublisher(sources).switchMap((Function)Functions.identity());
     }
 
@@ -4401,7 +4401,7 @@ public static <T> Flowable<T> switchOnNext(@NonNull Publisher<? extends Publishe
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> switchOnNextDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources) {
+    public static <T> Flowable<T> switchOnNextDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources) {
         return switchOnNextDelayError(sources, bufferSize());
     }
 
@@ -4445,8 +4445,8 @@ public static <T> Flowable<T> switchOnNextDelayError(@NonNull Publisher<? extend
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> switchOnNextDelayError(@NonNull Publisher<? extends Publisher<? extends T>> sources, int prefetch) {
-        return fromPublisher(sources).switchMapDelayError(Functions.<Publisher<? extends T>>identity(), prefetch);
+    public static <T> Flowable<T> switchOnNextDelayError(@NonNull Publisher<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, int prefetch) {
+        return fromPublisher(sources).switchMapDelayError(Functions.<Publisher<@NonNull ? extends T>>identity(), prefetch);
     }
 
     /**
@@ -4575,7 +4575,7 @@ public static <T> Flowable<T> unsafeCreate(@NonNull Publisher<T> onSubscribe) {
     @NonNull
     public static <T, D> Flowable<T> using(
             @NonNull Supplier<? extends D> resourceSupplier,
-            @NonNull Function<? super D, ? extends Publisher<? extends T>> sourceSupplier,
+            @NonNull Function<? super D, ? extends Publisher<@NonNull ? extends T>> sourceSupplier,
             @NonNull Consumer<? super D> resourceDisposer) {
         return using(resourceSupplier, sourceSupplier, resourceDisposer, true);
     }
@@ -4618,7 +4618,7 @@ public static <T, D> Flowable<T> using(
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T, D> Flowable<T> using(
             @NonNull Supplier<? extends D> resourceSupplier,
-            @NonNull Function<? super D, ? extends Publisher<? extends T>> sourceSupplier,
+            @NonNull Function<? super D, ? extends Publisher<@NonNull ? extends T>> sourceSupplier,
             @NonNull Consumer<? super D> resourceDisposer,
             boolean eager) {
         Objects.requireNonNull(resourceSupplier, "resourceSupplier is null");
@@ -4676,7 +4676,7 @@ public static <T, D> Flowable<T> using(
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, R> Flowable<R> zip(@NonNull Iterable<? extends Publisher<? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
+    public static <T, R> Flowable<R> zip(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
         Objects.requireNonNull(zipper, "zipper is null");
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new FlowableZip<>(null, sources, zipper, bufferSize(), false));
@@ -4737,7 +4737,7 @@ public static <T, R> Flowable<R> zip(@NonNull Iterable<? extends Publisher<? ext
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, R> Flowable<R> zip(@NonNull Iterable<? extends Publisher<? extends T>> sources,
+    public static <T, R> Flowable<R> zip(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> zipper, boolean delayError,
             int bufferSize) {
         Objects.requireNonNull(zipper, "zipper is null");
@@ -4800,7 +4800,7 @@ public static <T, R> Flowable<R> zip(@NonNull Iterable<? extends Publisher<? ext
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
             @NonNull BiFunction<? super T1, ? super T2, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -4863,7 +4863,7 @@ public static <T1, T2, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
             @NonNull BiFunction<? super T1, ? super T2, ? extends R> zipper, boolean delayError) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -4928,7 +4928,7 @@ public static <T1, T2, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2,
             @NonNull BiFunction<? super T1, ? super T2, ? extends R> zipper, boolean delayError, int bufferSize) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -4994,7 +4994,7 @@ public static <T1, T2, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
             @NonNull Function3<? super T1, ? super T2, ? super T3, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5065,8 +5065,8 @@ public static <T1, T2, T3, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4,
             @NonNull Function4<? super T1, ? super T2, ? super T3, ? super T4, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5141,8 +5141,8 @@ public static <T1, T2, T3, T4, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4, @NonNull Publisher<? extends T5> source5,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4, @NonNull Publisher<@NonNull ? extends T5> source5,
             @NonNull Function5<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5221,8 +5221,8 @@ public static <T1, T2, T3, T4, T5, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4, @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4, @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
             @NonNull Function6<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5305,9 +5305,9 @@ public static <T1, T2, T3, T4, T5, T6, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4, @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4, @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7,
             @NonNull Function7<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5394,9 +5394,9 @@ public static <T1, T2, T3, T4, T5, T6, T7, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4, @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7, @NonNull Publisher<? extends T8> source8,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4, @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7, @NonNull Publisher<@NonNull ? extends T8> source8,
             @NonNull Function8<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? extends R> zipper) {
         Objects.requireNonNull(source1, "source1 is null");
         Objects.requireNonNull(source2, "source2 is null");
@@ -5488,9 +5488,9 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, R> Flowable<R> zip(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Flowable<R> zip(
-            @NonNull Publisher<? extends T1> source1, @NonNull Publisher<? extends T2> source2, @NonNull Publisher<? extends T3> source3,
-            @NonNull Publisher<? extends T4> source4, @NonNull Publisher<? extends T5> source5, @NonNull Publisher<? extends T6> source6,
-            @NonNull Publisher<? extends T7> source7, @NonNull Publisher<? extends T8> source8, @NonNull Publisher<? extends T9> source9,
+            @NonNull Publisher<@NonNull ? extends T1> source1, @NonNull Publisher<@NonNull ? extends T2> source2, @NonNull Publisher<@NonNull ? extends T3> source3,
+            @NonNull Publisher<@NonNull ? extends T4> source4, @NonNull Publisher<@NonNull ? extends T5> source5, @NonNull Publisher<@NonNull ? extends T6> source6,
+            @NonNull Publisher<@NonNull ? extends T7> source7, @NonNull Publisher<@NonNull ? extends T8> source8, @NonNull Publisher<@NonNull ? extends T9> source9,
             @NonNull Function9<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8, ? super T9, ? extends R> zipper) {
 
         Objects.requireNonNull(source1, "source1 is null");
@@ -5563,7 +5563,7 @@ public static <T1, T2, T3, T4, T5, T6, T7, T8, T9, R> Flowable<R> zip(
     @SchedulerSupport(SchedulerSupport.NONE)
     @SafeVarargs
     public static <T, R> Flowable<R> zipArray(@NonNull Function<? super Object[], ? extends R> zipper,
-            boolean delayError, int bufferSize, @NonNull Publisher<? extends T>... sources) {
+            boolean delayError, int bufferSize, @NonNull Publisher<@NonNull ? extends T>... sources) {
         Objects.requireNonNull(sources, "sources is null");
         if (sources.length == 0) {
             return empty();
@@ -5631,7 +5631,7 @@ public final Single<Boolean> all(@NonNull Predicate<? super T> predicate) {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> ambWith(@NonNull Publisher<? extends T> other) {
+    public final Flowable<T> ambWith(@NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return ambArray(this, other);
     }
@@ -6343,7 +6343,7 @@ public final void blockingSubscribe(@NonNull Consumer<? super T> onNext, @NonNul
      */
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final void blockingSubscribe(@NonNull Subscriber<? super T> subscriber) {
+    public final void blockingSubscribe(@NonNull Subscriber<@NonNull ? super T> subscriber) {
         Objects.requireNonNull(subscriber, "subscriber is null");
         FlowableBlockingSubscribe.subscribe(this, subscriber);
     }
@@ -6862,7 +6862,7 @@ public final Flowable<List<T>> buffer(long timespan, @NonNull TimeUnit unit, @No
     @NonNull
     public final <TOpening, TClosing> Flowable<List<T>> buffer(
             @NonNull Flowable<? extends TOpening> openingIndicator,
-            @NonNull Function<? super TOpening, ? extends Publisher<? extends TClosing>> closingIndicator) {
+            @NonNull Function<? super TOpening, ? extends Publisher<@NonNull ? extends TClosing>> closingIndicator) {
         return buffer(openingIndicator, closingIndicator, ArrayListSupplier.asSupplier());
     }
 
@@ -6904,7 +6904,7 @@ public final <TOpening, TClosing> Flowable<List<T>> buffer(
     @NonNull
     public final <TOpening, TClosing, U extends Collection<? super T>> Flowable<U> buffer(
             @NonNull Flowable<? extends TOpening> openingIndicator,
-            @NonNull Function<? super TOpening, ? extends Publisher<? extends TClosing>> closingIndicator,
+            @NonNull Function<? super TOpening, ? extends Publisher<@NonNull ? extends TClosing>> closingIndicator,
             @NonNull Supplier<U> bufferSupplier) {
         Objects.requireNonNull(openingIndicator, "openingIndicator is null");
         Objects.requireNonNull(closingIndicator, "closingIndicator is null");
@@ -7335,7 +7335,7 @@ public final <R> Flowable<R> compose(@NonNull FlowableTransformer<? super T, ? e
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return concatMap(mapper, 2);
     }
 
@@ -7377,7 +7377,7 @@ public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Pu
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, int prefetch) {
+    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         if (this instanceof ScalarSupplier) {
@@ -7432,7 +7432,7 @@ public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Pu
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
-    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, int prefetch, @NonNull Scheduler scheduler) {
+    public final <R> Flowable<R> concatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int prefetch, @NonNull Scheduler scheduler) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         Objects.requireNonNull(scheduler, "scheduler is null");
@@ -7643,7 +7643,7 @@ public final Completable concatMapCompletableDelayError(@NonNull Function<? supe
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return concatMapDelayError(mapper, true, 2);
     }
 
@@ -7684,7 +7684,7 @@ public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ?
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean tillTheEnd, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -7738,7 +7738,7 @@ public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ?
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
-    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean tillTheEnd, int prefetch, @NonNull Scheduler scheduler) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -7771,7 +7771,7 @@ public final <R> Flowable<R> concatMapDelayError(@NonNull Function<? super T, ?
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return concatMapEager(mapper, bufferSize(), bufferSize());
     }
 
@@ -7803,7 +7803,7 @@ public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? exten
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             int maxConcurrency, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
@@ -7839,7 +7839,7 @@ public final <R> Flowable<R> concatMapEager(@NonNull Function<? super T, ? exten
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean tillTheEnd) {
         return concatMapEagerDelayError(mapper, tillTheEnd, bufferSize(), bufferSize());
     }
@@ -7877,7 +7877,7 @@ public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean tillTheEnd, int maxConcurrency, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
@@ -7912,7 +7912,7 @@ public final <R> Flowable<R> concatMapEagerDelayError(@NonNull Function<? super
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U> Flowable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Flowable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         return concatMapIterable(mapper, 2);
     }
 
@@ -7946,7 +7946,7 @@ public final <U> Flowable<U> concatMapIterable(@NonNull Function<? super T, ? ex
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> Flowable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper, int prefetch) {
+    public final <U> Flowable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableFlattenIterable<>(this, mapper, prefetch));
@@ -8357,7 +8357,7 @@ public final <R> Flowable<R> concatMapSingleDelayError(@NonNull Function<? super
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> concatWith(@NonNull Publisher<? extends T> other) {
+    public final Flowable<T> concatWith(@NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return concat(this, other);
     }
@@ -9508,7 +9508,7 @@ public final Flowable<T> doOnEach(@NonNull Consumer<@NonNull ? super Notificatio
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> doOnEach(@NonNull Subscriber<? super T> subscriber) {
+    public final Flowable<T> doOnEach(@NonNull Subscriber<@NonNull ? super T> subscriber) {
         Objects.requireNonNull(subscriber, "subscriber is null");
         return doOnEach(
                 FlowableInternalHelper.subscriberOnNext(subscriber),
@@ -9929,7 +9929,7 @@ public final Single<T> firstOrError() {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return flatMap(mapper, false, bufferSize(), bufferSize());
     }
 
@@ -9966,7 +9966,7 @@ public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, boolean delayErrors) {
+    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, boolean delayErrors) {
         return flatMap(mapper, delayErrors, bufferSize(), bufferSize());
     }
 
@@ -10005,7 +10005,7 @@ public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, int maxConcurrency) {
+    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int maxConcurrency) {
         return flatMap(mapper, false, maxConcurrency, bufferSize());
     }
 
@@ -10046,7 +10046,7 @@ public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, boolean delayErrors, int maxConcurrency) {
+    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, boolean delayErrors, int maxConcurrency) {
         return flatMap(mapper, delayErrors, maxConcurrency, bufferSize());
     }
 
@@ -10090,7 +10090,7 @@ public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publ
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+    public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean delayErrors, int maxConcurrency, int bufferSize) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
@@ -10141,9 +10141,9 @@ public final <R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publ
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> flatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> onNextMapper,
-            @NonNull Function<? super Throwable, ? extends Publisher<? extends R>> onErrorMapper,
-            @NonNull Supplier<? extends Publisher<? extends R>> onCompleteSupplier) {
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> onNextMapper,
+            @NonNull Function<? super Throwable, ? extends Publisher<@NonNull ? extends R>> onErrorMapper,
+            @NonNull Supplier<? extends Publisher<@NonNull ? extends R>> onCompleteSupplier) {
         Objects.requireNonNull(onNextMapper, "onNextMapper is null");
         Objects.requireNonNull(onErrorMapper, "onErrorMapper is null");
         Objects.requireNonNull(onCompleteSupplier, "onCompleteSupplier is null");
@@ -10190,9 +10190,9 @@ public final <R> Flowable<R> flatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> Flowable<R> flatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> onNextMapper,
-            @NonNull Function<Throwable, ? extends Publisher<? extends R>> onErrorMapper,
-            @NonNull Supplier<? extends Publisher<? extends R>> onCompleteSupplier,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> onNextMapper,
+            @NonNull Function<Throwable, ? extends Publisher<@NonNull ? extends R>> onErrorMapper,
+            @NonNull Supplier<? extends Publisher<@NonNull ? extends R>> onCompleteSupplier,
             int maxConcurrency) {
         Objects.requireNonNull(onNextMapper, "onNextMapper is null");
         Objects.requireNonNull(onErrorMapper, "onErrorMapper is null");
@@ -10234,7 +10234,7 @@ public final <R> Flowable<R> flatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends U>> mapper,
+    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner) {
         return flatMap(mapper, combiner, false, bufferSize(), bufferSize());
     }
@@ -10275,7 +10275,7 @@ public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends P
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends U>> mapper,
+    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner, boolean delayErrors) {
         return flatMap(mapper, combiner, delayErrors, bufferSize(), bufferSize());
     }
@@ -10321,7 +10321,7 @@ public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends P
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends U>> mapper,
+    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner, boolean delayErrors, int maxConcurrency) {
         return flatMap(mapper, combiner, delayErrors, maxConcurrency, bufferSize());
     }
@@ -10369,7 +10369,7 @@ public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends P
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends U>> mapper,
+    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner, boolean delayErrors, int maxConcurrency, int bufferSize) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -10416,7 +10416,7 @@ public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends P
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends U>> mapper,
+    public final <U, R> Flowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner, int maxConcurrency) {
         return flatMap(mapper, combiner, false, maxConcurrency, bufferSize());
     }
@@ -10498,7 +10498,7 @@ public final Completable flatMapCompletable(@NonNull Function<? super T, ? exten
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         return flatMapIterable(mapper, bufferSize());
     }
 
@@ -10532,7 +10532,7 @@ public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? exte
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper, int bufferSize) {
+    public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper, int bufferSize) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new FlowableFlattenIterable<>(this, mapper, bufferSize));
@@ -10572,7 +10572,7 @@ public final <U> Flowable<U> flatMapIterable(@NonNull Function<? super T, ? exte
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, V> Flowable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper,
+    public final <U, V> Flowable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends V> combiner) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -10617,7 +10617,7 @@ public final <U, V> Flowable<V> flatMapIterable(@NonNull Function<? super T, ? e
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, V> Flowable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper,
+    public final <U, V> Flowable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends V> combiner, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -11349,9 +11349,9 @@ public final <K, V> Flowable<GroupedFlowable<K, V>> groupBy(@NonNull Function<?
     @BackpressureSupport(BackpressureKind.ERROR)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <TRight, TLeftEnd, TRightEnd, R> Flowable<R> groupJoin(
-            @NonNull Publisher<? extends TRight> other,
-            @NonNull Function<? super T, ? extends Publisher<TLeftEnd>> leftEnd,
-            @NonNull Function<? super TRight, ? extends Publisher<TRightEnd>> rightEnd,
+            @NonNull Publisher<@NonNull ? extends TRight> other,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull TLeftEnd>> leftEnd,
+            @NonNull Function<? super TRight, ? extends Publisher<@NonNull TRightEnd>> rightEnd,
             @NonNull BiFunction<? super T, ? super Flowable<TRight>, ? extends R> resultSelector) {
         Objects.requireNonNull(other, "other is null");
         Objects.requireNonNull(leftEnd, "leftEnd is null");
@@ -11475,9 +11475,9 @@ public final Single<Boolean> isEmpty() {
     @BackpressureSupport(BackpressureKind.ERROR)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <TRight, TLeftEnd, TRightEnd, R> Flowable<R> join(
-            @NonNull Publisher<? extends TRight> other,
-            @NonNull Function<? super T, ? extends Publisher<TLeftEnd>> leftEnd,
-            @NonNull Function<? super TRight, ? extends Publisher<TRightEnd>> rightEnd,
+            @NonNull Publisher<@NonNull ? extends TRight> other,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull TLeftEnd>> leftEnd,
+            @NonNull Function<? super TRight, ? extends Publisher<@NonNull TRightEnd>> rightEnd,
             @NonNull BiFunction<? super T, ? super TRight, ? extends R> resultSelector) {
         Objects.requireNonNull(other, "other is null");
         Objects.requireNonNull(leftEnd, "leftEnd is null");
@@ -11801,7 +11801,7 @@ public final Flowable<Notification<T>> materialize() {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> mergeWith(@NonNull Publisher<? extends T> other) {
+    public final Flowable<T> mergeWith(@NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return merge(this, other);
     }
@@ -12478,7 +12478,7 @@ public final Flowable<T> onBackpressureLatest() {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> onErrorResumeNext(@NonNull Function<? super Throwable, ? extends Publisher<? extends T>> resumeFunction) {
+    public final Flowable<T> onErrorResumeNext(@NonNull Function<? super Throwable, ? extends Publisher<@NonNull ? extends T>> resumeFunction) {
         Objects.requireNonNull(resumeFunction, "resumeFunction is null");
         return RxJavaPlugins.onAssembly(new FlowableOnErrorNext<>(this, resumeFunction));
     }
@@ -12523,7 +12523,7 @@ public final Flowable<T> onErrorResumeNext(@NonNull Function<? super Throwable,
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> onErrorResumeWith(@NonNull Publisher<? extends T> next) {
+    public final Flowable<T> onErrorResumeWith(@NonNull Publisher<@NonNull ? extends T> next) {
         Objects.requireNonNull(next, "next is null");
         return onErrorResumeNext(Functions.justFunction(next));
     }
@@ -12822,7 +12822,7 @@ public final <R> Flowable<R> publish(@NonNull Function<? super Flowable<T>, ? ex
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> publish(@NonNull Function<? super Flowable<T>, ? extends Publisher<? extends R>> selector, int prefetch) {
+    public final <R> Flowable<R> publish(@NonNull Function<? super Flowable<T>, ? extends Publisher<@NonNull ? extends R>> selector, int prefetch) {
         Objects.requireNonNull(selector, "selector is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowablePublishMulticast<>(this, selector, prefetch, false));
@@ -13153,7 +13153,7 @@ public final Flowable<T> repeatUntil(@NonNull BooleanSupplier stop) {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<?>> handler) {
+    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<@NonNull ?>> handler) {
         Objects.requireNonNull(handler, "handler is null");
         return RxJavaPlugins.onAssembly(new FlowableRepeatWhen<>(this, handler));
     }
@@ -14183,7 +14183,7 @@ public final Flowable<T> retryUntil(@NonNull BooleanSupplier stop) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final Flowable<T> retryWhen(
-            @NonNull Function<? super Flowable<Throwable>, ? extends Publisher<?>> handler) {
+            @NonNull Function<? super Flowable<Throwable>, ? extends Publisher<@NonNull ?>> handler) {
         Objects.requireNonNull(handler, "handler is null");
 
         return RxJavaPlugins.onAssembly(new FlowableRetryWhen<>(this, handler));
@@ -14205,10 +14205,10 @@ public final Flowable<T> retryWhen(
      */
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final void safeSubscribe(@NonNull Subscriber<? super T> subscriber) {
+    public final void safeSubscribe(@NonNull Subscriber<@NonNull ? super T> subscriber) {
         Objects.requireNonNull(subscriber, "subscriber is null");
         if (subscriber instanceof SafeSubscriber) {
-            subscribe((SafeSubscriber<? super T>)subscriber);
+            subscribe((SafeSubscriber<@NonNull ? super T>)subscriber);
         } else {
             subscribe(new SafeSubscriber<>(subscriber));
         }
@@ -15169,7 +15169,7 @@ public final Flowable<T> sorted(@NonNull Comparator<@NonNull ? super T> comparat
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Flowable<T> startWithIterable(@NonNull Iterable<? extends T> items) {
+    public final Flowable<T> startWithIterable(@NonNull Iterable<@NonNull ? extends T> items) {
         return concatArray(fromIterable(items), this);
     }
 
@@ -15198,7 +15198,7 @@ public final Flowable<T> startWithIterable(@NonNull Iterable<? extends T> items)
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> startWith(@NonNull Publisher<? extends T> other) {
+    public final Flowable<T> startWith(@NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return concatArray(other, this);
     }
@@ -15402,9 +15402,9 @@ public final Disposable subscribe(@NonNull Consumer<? super T> onNext, @NonNull
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @Override
-    public final void subscribe(@NonNull Subscriber<? super T> subscriber) {
+    public final void subscribe(@NonNull Subscriber<@NonNull ? super T> subscriber) {
         if (subscriber instanceof FlowableSubscriber) {
-            subscribe((FlowableSubscriber<? super T>)subscriber);
+            subscribe((FlowableSubscriber<@NonNull ? super T>)subscriber);
         } else {
             Objects.requireNonNull(subscriber, "subscriber is null");
             subscribe(new StrictSubscriber<>(subscriber));
@@ -15451,10 +15451,10 @@ public final void subscribe(@NonNull Subscriber<? super T> subscriber) {
      */
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final void subscribe(@NonNull FlowableSubscriber<? super T> subscriber) {
+    public final void subscribe(@NonNull FlowableSubscriber<@NonNull ? super T> subscriber) {
         Objects.requireNonNull(subscriber, "subscriber is null");
         try {
-            Subscriber<? super T> flowableSubscriber = RxJavaPlugins.onSubscribe(this, subscriber);
+            Subscriber<@NonNull ? super T> flowableSubscriber = RxJavaPlugins.onSubscribe(this, subscriber);
 
             Objects.requireNonNull(flowableSubscriber, "The RxJavaPlugins.onSubscribe hook returned a null FlowableSubscriber. Please check the handler provided to RxJavaPlugins.setOnFlowableSubscribe for invalid null returns. Further reading: https://github.com/ReactiveX/RxJava/wiki/Plugins");
 
@@ -15481,7 +15481,7 @@ public final void subscribe(@NonNull FlowableSubscriber<? super T> subscriber) {
      * applied by {@link #subscribe(Subscriber)} before this method gets called.
      * @param subscriber the incoming {@code Subscriber}, never {@code null}
      */
-    protected abstract void subscribeActual(@NonNull Subscriber<? super T> subscriber);
+    protected abstract void subscribeActual(@NonNull Subscriber<@NonNull ? super T> subscriber);
 
     /**
      * Subscribes a given {@link Subscriber} (subclass) to this {@code Flowable} and returns the given
@@ -15514,7 +15514,7 @@ public final void subscribe(@NonNull FlowableSubscriber<? super T> subscriber) {
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull E extends Subscriber<? super T>> E subscribeWith(E subscriber) {
+    public final <@NonNull E extends Subscriber<@NonNull ? super T>> E subscribeWith(E subscriber) {
         subscribe(subscriber);
         return subscriber;
     }
@@ -15620,7 +15620,7 @@ public final Flowable<T> subscribeOn(@NonNull Scheduler scheduler, boolean reque
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Flowable<T> switchIfEmpty(@NonNull Publisher<? extends T> other) {
+    public final Flowable<T> switchIfEmpty(@NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return RxJavaPlugins.onAssembly(new FlowableSwitchIfEmpty<>(this, other));
     }
@@ -15657,7 +15657,7 @@ public final Flowable<T> switchIfEmpty(@NonNull Publisher<? extends T> other) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> switchMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> switchMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return switchMap(mapper, bufferSize());
     }
 
@@ -15696,7 +15696,7 @@ public final <R> Flowable<R> switchMap(@NonNull Function<? super T, ? extends Pu
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> switchMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, int bufferSize) {
+    public final <R> Flowable<R> switchMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int bufferSize) {
         return switchMap0(mapper, bufferSize, false);
     }
 
@@ -15829,7 +15829,7 @@ public final Completable switchMapCompletableDelayError(@NonNull Function<? supe
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> switchMapDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> switchMapDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return switchMapDelayError(mapper, bufferSize());
     }
 
@@ -15870,11 +15870,11 @@ public final <R> Flowable<R> switchMapDelayError(@NonNull Function<? super T, ?
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Flowable<R> switchMapDelayError(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, int bufferSize) {
+    public final <R> Flowable<R> switchMapDelayError(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int bufferSize) {
         return switchMap0(mapper, bufferSize, true);
     }
 
-    <R> Flowable<R> switchMap0(Function<? super T, ? extends Publisher<? extends R>> mapper, int bufferSize, boolean delayError) {
+    <R> Flowable<R> switchMap0(Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, int bufferSize, boolean delayError) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         if (this instanceof ScalarSupplier) {
@@ -17156,7 +17156,7 @@ public final <V> Flowable<T> timeout(@NonNull Function<? super T, ? extends Publ
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <V> Flowable<T> timeout(@NonNull Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator, @NonNull Publisher<? extends T> other) {
+    public final <V> Flowable<T> timeout(@NonNull Function<? super T, ? extends Publisher<@NonNull V>> itemTimeoutIndicator, @NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return timeout0(null, itemTimeoutIndicator, other);
     }
@@ -17222,7 +17222,7 @@ public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit) {
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.COMPUTATION)
-    public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit, @NonNull Publisher<? extends T> other) {
+    public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit, @NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return timeout0(timeout, unit, other, Schedulers.computation());
     }
@@ -17261,7 +17261,7 @@ public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit, @NonNull
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.CUSTOM)
-    public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit, @NonNull Scheduler scheduler, @NonNull Publisher<? extends T> other) {
+    public final Flowable<T> timeout(long timeout, @NonNull TimeUnit unit, @NonNull Scheduler scheduler, @NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(other, "other is null");
         return timeout0(timeout, unit, other, scheduler);
     }
@@ -17384,13 +17384,13 @@ public final <U, V> Flowable<T> timeout(@NonNull Publisher<U> firstTimeoutIndica
     public final <U, V> Flowable<T> timeout(
             @NonNull Publisher<U> firstTimeoutIndicator,
             @NonNull Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator,
-            @NonNull Publisher<? extends T> other) {
+            @NonNull Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(firstTimeoutIndicator, "firstTimeoutIndicator is null");
         Objects.requireNonNull(other, "other is null");
         return timeout0(firstTimeoutIndicator, itemTimeoutIndicator, other);
     }
 
-    private Flowable<T> timeout0(long timeout, TimeUnit unit, Publisher<? extends T> other,
+    private Flowable<T> timeout0(long timeout, TimeUnit unit, Publisher<@NonNull ? extends T> other,
             Scheduler scheduler) {
         Objects.requireNonNull(unit, "unit is null");
         Objects.requireNonNull(scheduler, "scheduler is null");
@@ -17399,8 +17399,8 @@ private Flowable<T> timeout0(long timeout, TimeUnit unit, Publisher<? extends T>
 
     private <U, V> Flowable<T> timeout0(
             Publisher<U> firstTimeoutIndicator,
-            Function<? super T, ? extends Publisher<V>> itemTimeoutIndicator,
-                    Publisher<? extends T> other) {
+            Function<? super T, ? extends Publisher<@NonNull V>> itemTimeoutIndicator,
+                    Publisher<@NonNull ? extends T> other) {
         Objects.requireNonNull(itemTimeoutIndicator, "itemTimeoutIndicator is null");
         return RxJavaPlugins.onAssembly(new FlowableTimeout<>(this, firstTimeoutIndicator, itemTimeoutIndicator, other));
     }
@@ -18923,7 +18923,7 @@ public final <U, V> Flowable<Flowable<T>> window(
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, @NonNull R> Flowable<R> withLatestFrom(@NonNull Publisher<? extends U> other,
+    public final <U, @NonNull R> Flowable<R> withLatestFrom(@NonNull Publisher<@NonNull ? extends U> other,
             @NonNull BiFunction<? super T, ? super U, ? extends R> combiner) {
         Objects.requireNonNull(other, "other is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -19093,7 +19093,7 @@ public final <U, V> Flowable<Flowable<T>> window(
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <@NonNull R> Flowable<R> withLatestFrom(@NonNull Publisher<?>[] others, @NonNull Function<? super Object[], R> combiner) {
+    public final <@NonNull R> Flowable<R> withLatestFrom(@NonNull Publisher<@NonNull ?>[] others, @NonNull Function<? super Object[], R> combiner) {
         Objects.requireNonNull(others, "others is null");
         Objects.requireNonNull(combiner, "combiner is null");
         return RxJavaPlugins.onAssembly(new FlowableWithLatestFromMany<>(this, others, combiner));
@@ -19127,7 +19127,7 @@ public final <U, V> Flowable<Flowable<T>> window(
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> withLatestFrom(@NonNull Iterable<? extends Publisher<?>> others, @NonNull Function<? super Object[], R> combiner) {
+    public final <R> Flowable<R> withLatestFrom(@NonNull Iterable<@NonNull ? extends Publisher<@NonNull ?>> others, @NonNull Function<? super Object[], R> combiner) {
         Objects.requireNonNull(others, "others is null");
         Objects.requireNonNull(combiner, "combiner is null");
         return RxJavaPlugins.onAssembly(new FlowableWithLatestFromMany<>(this, others, combiner));
@@ -19168,7 +19168,7 @@ public final <R> Flowable<R> withLatestFrom(@NonNull Iterable<? extends Publishe
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, R> Flowable<R> zipWith(@NonNull Iterable<U> other,  @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
+    public final <@NonNull U, R> Flowable<R> zipWith(@NonNull Iterable<U> other,  @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
         Objects.requireNonNull(other, "other is null");
         Objects.requireNonNull(zipper, "zipper is null");
         return RxJavaPlugins.onAssembly(new FlowableZipIterable<>(this, other, zipper));
@@ -19218,7 +19218,7 @@ public final <U, R> Flowable<R> zipWith(@NonNull Iterable<U> other,  @NonNull Bi
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<? extends U> other, @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
+    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<@NonNull ? extends U> other, @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
         Objects.requireNonNull(other, "other is null");
         return zip(this, other, zipper);
     }
@@ -19270,7 +19270,7 @@ public final <U, R> Flowable<R> zipWith(@NonNull Publisher<? extends U> other, @
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<? extends U> other,
+    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<@NonNull ? extends U> other,
             @NonNull BiFunction<? super T, ? super U, ? extends R> zipper, boolean delayError) {
         return zip(this, other, zipper, delayError);
     }
@@ -19325,7 +19325,7 @@ public final <U, R> Flowable<R> zipWith(@NonNull Publisher<? extends U> other,
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<? extends U> other,
+    public final <U, R> Flowable<R> zipWith(@NonNull Publisher<@NonNull ? extends U> other,
             @NonNull BiFunction<? super T, ? super U, ? extends R> zipper, boolean delayError, int bufferSize) {
         return zip(this, other, zipper, delayError, bufferSize);
     }
@@ -19912,7 +19912,7 @@ public final Stream<T> blockingStream(int prefetch) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Flowable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper) {
+    public final <@NonNull R> Flowable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper) {
         return flatMapStream(mapper, bufferSize());
     }
 
@@ -19967,7 +19967,7 @@ public final Stream<T> blockingStream(int prefetch) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Flowable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper, int prefetch) {
+    public final <@NonNull R> Flowable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapStream<>(this, mapper, prefetch));
@@ -20023,7 +20023,7 @@ public final Stream<T> blockingStream(int prefetch) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Flowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper) {
+    public final <@NonNull R> Flowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper) {
         return flatMapStream(mapper, bufferSize());
     }
 
@@ -20078,7 +20078,7 @@ public final Stream<T> blockingStream(int prefetch) {
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Flowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper, int prefetch) {
+    public final <@NonNull R> Flowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapStream<>(this, mapper, prefetch));
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableConverter.java b/src/main/java/io/reactivex/rxjava3/core/FlowableConverter.java
index 92733c3c1e..d0b1814fb8 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableConverter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableConverter.java
@@ -24,13 +24,12 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface FlowableConverter<T, R> {
+public interface FlowableConverter<@NonNull T, @NonNull R> {
     /**
      * Applies a function to the upstream {@link Flowable} and returns a converted value of type {@code R}.
      *
      * @param upstream the upstream {@code Flowable} instance
      * @return the converted value
      */
-    @NonNull
     R apply(@NonNull Flowable<T> upstream);
 }
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableEmitter.java b/src/main/java/io/reactivex/rxjava3/core/FlowableEmitter.java
index 1221721f29..8304edca71 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableEmitter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableEmitter.java
@@ -15,7 +15,7 @@
 
 import io.reactivex.rxjava3.annotations.*;
 import io.reactivex.rxjava3.disposables.Disposable;
-import io.reactivex.rxjava3.functions.Cancellable;
+import io.reactivex.rxjava3.functions.*;
 
 /**
  * Abstraction over a Reactive Streams {@link org.reactivestreams.Subscriber} that allows associating
@@ -48,7 +48,7 @@
  *
  * @param <T> the value type to emit
  */
-public interface FlowableEmitter<T> extends Emitter<T> {
+public interface FlowableEmitter<@NonNull T> extends Emitter<T> {
 
     /**
      * Sets a Disposable on this emitter; any previous {@link Disposable}
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableOnSubscribe.java b/src/main/java/io/reactivex/rxjava3/core/FlowableOnSubscribe.java
index 156b9f2dc7..129c6ac7b6 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableOnSubscribe.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableOnSubscribe.java
@@ -22,7 +22,7 @@
  * @param <T> the value type pushed
  */
 @FunctionalInterface
-public interface FlowableOnSubscribe<T> {
+public interface FlowableOnSubscribe<@NonNull T> {
 
     /**
      * Called for each {@link org.reactivestreams.Subscriber Subscriber} that subscribes.
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableOperator.java b/src/main/java/io/reactivex/rxjava3/core/FlowableOperator.java
index 5b5855ea2f..aed58cff89 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableOperator.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableOperator.java
@@ -24,7 +24,7 @@
  * @param <Upstream> the value type of the upstream
  */
 @FunctionalInterface
-public interface FlowableOperator<Downstream, Upstream> {
+public interface FlowableOperator<@NonNull Downstream, @NonNull Upstream> {
     /**
      * Applies a function to the child {@link Subscriber} and returns a new parent {@code Subscriber}.
      * @param subscriber the child {@code Subscriber} instance
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableSubscriber.java b/src/main/java/io/reactivex/rxjava3/core/FlowableSubscriber.java
index 23449fbedc..38b5bf3459 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableSubscriber.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableSubscriber.java
@@ -25,7 +25,7 @@
  * @param <T> the value type
  * @since 2.2
  */
-public interface FlowableSubscriber<T> extends Subscriber<T> {
+public interface FlowableSubscriber<@NonNull T> extends Subscriber<T> {
 
     /**
      * Implementors of this method should make sure everything that needs
diff --git a/src/main/java/io/reactivex/rxjava3/core/FlowableTransformer.java b/src/main/java/io/reactivex/rxjava3/core/FlowableTransformer.java
index 3b98a97dad..8aa444afcc 100644
--- a/src/main/java/io/reactivex/rxjava3/core/FlowableTransformer.java
+++ b/src/main/java/io/reactivex/rxjava3/core/FlowableTransformer.java
@@ -24,7 +24,7 @@
  * @param <Downstream> the downstream value type
  */
 @FunctionalInterface
-public interface FlowableTransformer<Upstream, Downstream> {
+public interface FlowableTransformer<@NonNull Upstream, @NonNull Downstream> {
     /**
      * Applies a function to the upstream {@link Flowable} and returns a {@link Publisher} with
      * optionally different element type.
diff --git a/src/main/java/io/reactivex/rxjava3/core/Maybe.java b/src/main/java/io/reactivex/rxjava3/core/Maybe.java
index 4892aa3ab0..6865558c05 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Maybe.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Maybe.java
@@ -129,7 +129,7 @@ public abstract class Maybe<T> implements MaybeSource<T> {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Maybe<T> amb(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Maybe<T> amb(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new MaybeAmb<>(null, sources));
     }
@@ -186,7 +186,7 @@ public static <T> Maybe<T> ambArray(@NonNull MaybeSource<? extends T>... sources
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concat(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new MaybeConcatIterable<>(sources));
     }
@@ -314,7 +314,7 @@ public static <T> Flowable<T> concat(
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return concat(sources, 2);
     }
 
@@ -343,7 +343,7 @@ public static <T> Flowable<T> concat(@NonNull Publisher<? extends MaybeSource<?
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends MaybeSource<? extends T>> sources, int prefetch) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources, int prefetch) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapPublisher(sources, MaybeToPublisher.instance(), prefetch, ErrorMode.IMMEDIATE));
@@ -469,7 +469,7 @@ public static <T> Flowable<T> concatArrayEager(@NonNull MaybeSource<? extends T>
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concatDelayError(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatDelayError(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return Flowable.fromIterable(sources).concatMapDelayError((Function)MaybeToPublisher.instance());
     }
@@ -497,7 +497,7 @@ public static <T> Flowable<T> concatDelayError(@NonNull Iterable<? extends Maybe
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatDelayError(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return Flowable.fromPublisher(sources).concatMapDelayError((Function)MaybeToPublisher.instance());
     }
 
@@ -525,7 +525,7 @@ public static <T> Flowable<T> concatDelayError(@NonNull Publisher<? extends Mayb
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return Flowable.fromIterable(sources).concatMapEager((Function)MaybeToPublisher.instance());
     }
 
@@ -555,7 +555,7 @@ public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends MaybeSourc
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return Flowable.fromPublisher(sources).concatMapEager((Function)MaybeToPublisher.instance());
     }
 
@@ -1020,7 +1020,7 @@ public static <T> Maybe<T> fromRunnable(@NonNull Runnable run) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return merge(Flowable.fromIterable(sources));
     }
 
@@ -1056,7 +1056,7 @@ public static <T> Flowable<T> merge(@NonNull Iterable<? extends MaybeSource<? ex
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return merge(sources, Integer.MAX_VALUE);
     }
 
@@ -1095,7 +1095,7 @@ public static <T> Flowable<T> merge(@NonNull Publisher<? extends MaybeSource<? e
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends MaybeSource<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources, int maxConcurrency) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, MaybeToPublisher.instance(), false, maxConcurrency, 1));
@@ -1413,7 +1413,7 @@ public static <T> Flowable<T> mergeArrayDelayError(@NonNull MaybeSource<? extend
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return Flowable.fromIterable(sources).flatMap((Function)MaybeToPublisher.instance(), true);
     }
 
@@ -1450,7 +1450,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends MaybeS
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends MaybeSource<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources) {
         return mergeDelayError(sources, Integer.MAX_VALUE);
     }
 
@@ -1491,7 +1491,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends Maybe
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends MaybeSource<? extends T>> sources, int maxConcurrency) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends MaybeSource<? extends T>> sources, int maxConcurrency) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, MaybeToPublisher.instance(), true, maxConcurrency, 1));
@@ -1917,7 +1917,7 @@ public static <T> Maybe<T> wrap(@NonNull MaybeSource<T> source) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, R> Maybe<R> zip(@NonNull Iterable<? extends MaybeSource<? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
+    public static <T, R> Maybe<R> zip(@NonNull Iterable<@NonNull ? extends MaybeSource<? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
         Objects.requireNonNull(zipper, "zipper is null");
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new MaybeZipIterable<>(sources, zipper));
@@ -3028,7 +3028,7 @@ public final Maybe<T> doOnError(@NonNull Consumer<? super Throwable> onError) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Maybe<T> doOnEvent(@NonNull BiConsumer<? super T, ? super Throwable> onEvent) {
+    public final Maybe<T> doOnEvent(@NonNull BiConsumer<@Nullable ? super T, @Nullable ? super Throwable> onEvent) {
         Objects.requireNonNull(onEvent, "onEvent is null");
         return RxJavaPlugins.onAssembly(new MaybeDoOnEvent<>(this, onEvent));
     }
@@ -3259,7 +3259,7 @@ public final <U, R> Maybe<R> flatMap(@NonNull Function<? super T, ? extends Mayb
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableFlowable<>(this, mapper));
     }
@@ -3286,7 +3286,7 @@ public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? ex
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> Observable<U> flattenAsObservable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Observable<U> flattenAsObservable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableObservable<>(this, mapper));
     }
@@ -3340,7 +3340,7 @@ public final <R> Observable<R> flatMapObservable(@NonNull Function<? super T, ?
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> flatMapPublisher(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> flatMapPublisher(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlatMapPublisher<>(this, mapper));
     }
@@ -4153,7 +4153,7 @@ public final Flowable<T> repeatUntil(@NonNull BooleanSupplier stop) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<?>> handler) {
+    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<@NonNull ?>> handler) {
         return toFlowable().repeatWhen(handler);
     }
 
@@ -4366,7 +4366,7 @@ public final Maybe<T> retryUntil(@NonNull BooleanSupplier stop) {
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
     public final Maybe<T> retryWhen(
-            @NonNull Function<? super Flowable<Throwable>, ? extends Publisher<?>> handler) {
+            @NonNull Function<? super Flowable<Throwable>, ? extends Publisher<@NonNull ?>> handler) {
         return toFlowable().retryWhen(handler).singleElement();
     }
 
@@ -5188,7 +5188,7 @@ public final CompletionStage<T> toCompletionStage(@Nullable T defaultItem) {
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T, ? extends Stream<? extends R>> mapper) {
+    public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlattenStreamAsFlowable<>(this, mapper));
     }
@@ -5228,7 +5228,7 @@ public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Observable<R> flattenStreamAsObservable(@NonNull Function<? super T, ? extends Stream<? extends R>> mapper) {
+    public final <R> Observable<R> flattenStreamAsObservable(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new MaybeFlattenStreamAsObservable<>(this, mapper));
     }
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeConverter.java b/src/main/java/io/reactivex/rxjava3/core/MaybeConverter.java
index eefe8c0973..221e8a671a 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeConverter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeConverter.java
@@ -24,7 +24,7 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface MaybeConverter<T, R> {
+public interface MaybeConverter<@NonNull T, @NonNull R> {
     /**
      * Applies a function to the upstream {@link Maybe} and returns a converted value of type {@code R}.
      *
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeEmitter.java b/src/main/java/io/reactivex/rxjava3/core/MaybeEmitter.java
index 7757e4b72a..eb7f1f7241 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeEmitter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeEmitter.java
@@ -15,7 +15,7 @@
 
 import io.reactivex.rxjava3.annotations.*;
 import io.reactivex.rxjava3.disposables.Disposable;
-import io.reactivex.rxjava3.functions.Cancellable;
+import io.reactivex.rxjava3.functions.*;
 
 /**
  * Abstraction over an RxJava {@link MaybeObserver} that allows associating
@@ -47,7 +47,7 @@
  *
  * @param <T> the value type to emit
  */
-public interface MaybeEmitter<T> {
+public interface MaybeEmitter<@NonNull T> {
 
     /**
      * Signal a success value.
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeObserver.java b/src/main/java/io/reactivex/rxjava3/core/MaybeObserver.java
index 52bee5923a..b0974fa97c 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeObserver.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeObserver.java
@@ -53,7 +53,7 @@
  *          the type of item the MaybeObserver expects to observe
  * @since 2.0
  */
-public interface MaybeObserver<T> {
+public interface MaybeObserver<@NonNull T> {
 
     /**
      * Provides the {@link MaybeObserver} with the means of cancelling (disposing) the
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeOnSubscribe.java b/src/main/java/io/reactivex/rxjava3/core/MaybeOnSubscribe.java
index 350d17af5d..f02756199e 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeOnSubscribe.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeOnSubscribe.java
@@ -22,7 +22,7 @@
  * @param <T> the value type pushed
  */
 @FunctionalInterface
-public interface MaybeOnSubscribe<T> {
+public interface MaybeOnSubscribe<@NonNull T> {
 
     /**
      * Called for each {@link MaybeObserver} that subscribes.
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeOperator.java b/src/main/java/io/reactivex/rxjava3/core/MaybeOperator.java
index 30da3286b6..4ddb18d1f7 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeOperator.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeOperator.java
@@ -21,7 +21,7 @@
  * @param <Upstream> the value type of the upstream
  */
 @FunctionalInterface
-public interface MaybeOperator<Downstream, Upstream> {
+public interface MaybeOperator<@NonNull Downstream, @NonNull Upstream> {
     /**
      * Applies a function to the child {@link MaybeObserver} and returns a new parent {@code MaybeObserver}.
      * @param observer the child {@code MaybeObserver} instance
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeSource.java b/src/main/java/io/reactivex/rxjava3/core/MaybeSource.java
index f066e5d32e..da9dbf0658 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeSource.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeSource.java
@@ -25,7 +25,7 @@
  * @since 2.0
  */
 @FunctionalInterface
-public interface MaybeSource<T> {
+public interface MaybeSource<@NonNull T> {
 
     /**
      * Subscribes the given {@link MaybeObserver} to this {@link MaybeSource} instance.
diff --git a/src/main/java/io/reactivex/rxjava3/core/MaybeTransformer.java b/src/main/java/io/reactivex/rxjava3/core/MaybeTransformer.java
index aebcb8353f..620076d722 100644
--- a/src/main/java/io/reactivex/rxjava3/core/MaybeTransformer.java
+++ b/src/main/java/io/reactivex/rxjava3/core/MaybeTransformer.java
@@ -22,7 +22,7 @@
  * @param <Downstream> the downstream value type
  */
 @FunctionalInterface
-public interface MaybeTransformer<Upstream, Downstream> {
+public interface MaybeTransformer<@NonNull Upstream, @NonNull Downstream> {
     /**
      * Applies a function to the upstream {@link Maybe} and returns a {@link MaybeSource} with
      * optionally different element type.
diff --git a/src/main/java/io/reactivex/rxjava3/core/Observable.java b/src/main/java/io/reactivex/rxjava3/core/Observable.java
index 788c758a4a..6b118b70b5 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Observable.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Observable.java
@@ -97,7 +97,7 @@
  * @see Flowable
  * @see io.reactivex.rxjava3.observers.DisposableObserver
  */
-public abstract class Observable<T> implements ObservableSource<T> {
+public abstract class Observable<@NonNull T> implements ObservableSource<T> {
 
     /**
      * Mirrors the one {@link ObservableSource} in an {@link Iterable} of several {@code ObservableSource}s that first either emits an item or sends
@@ -121,7 +121,7 @@ public abstract class Observable<T> implements ObservableSource<T> {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Observable<T> amb(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> amb(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new ObservableAmb<>(null, sources));
     }
@@ -214,7 +214,7 @@ public static int bufferSize() {
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
     public static <T, R> Observable<R> combineLatest(
-            @NonNull Iterable<? extends ObservableSource<? extends T>> sources,
+            @NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatest(sources, combiner, bufferSize());
     }
@@ -262,7 +262,7 @@ public static <T, R> Observable<R> combineLatest(
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     public static <T, R> Observable<R> combineLatest(
-            @NonNull Iterable<? extends ObservableSource<? extends T>> sources,
+            @NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -989,7 +989,7 @@ public static <T, R> Observable<R> combineLatestArrayDelayError(@NonNull Observa
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources,
+    public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner) {
         return combineLatestDelayError(sources, combiner, bufferSize());
     }
@@ -1037,7 +1037,7 @@ public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<? e
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources,
+    public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> combiner, int bufferSize) {
         Objects.requireNonNull(sources, "sources is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -1066,7 +1066,7 @@ public static <T, R> Observable<R> combineLatestDelayError(@NonNull Iterable<? e
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Observable<T> concat(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> concat(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return fromIterable(sources).concatMapDelayError((Function)Functions.identity(), false, bufferSize());
     }
@@ -1424,7 +1424,7 @@ public static <T> Observable<T> concatArrayEagerDelayError(int maxConcurrency, i
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Observable<T> concatDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> concatDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return concatDelayError(fromIterable(sources));
     }
@@ -1557,7 +1557,7 @@ public static <T> Observable<T> concatEager(@NonNull ObservableSource<? extends
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> concatEager(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> concatEager(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         return concatEager(sources, bufferSize(), bufferSize());
     }
 
@@ -1587,7 +1587,7 @@ public static <T> Observable<T> concatEager(@NonNull Iterable<? extends Observab
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> concatEager(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
+    public static <T> Observable<T> concatEager(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
         return fromIterable(sources).concatMapEagerDelayError((Function)Functions.identity(), false, maxConcurrency, bufferSize);
     }
 
@@ -1934,7 +1934,7 @@ public static <T> Observable<T> fromFuture(@NonNull Future<? extends T> future,
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Observable<T> fromIterable(@NonNull Iterable<? extends T> source) {
+    public static <T> Observable<T> fromIterable(@NonNull Iterable<@NonNull ? extends T> source) {
         Objects.requireNonNull(source, "source is null");
         return RxJavaPlugins.onAssembly(new ObservableFromIterable<>(source));
     }
@@ -1971,7 +1971,7 @@ public static <T> Observable<T> fromIterable(@NonNull Iterable<? extends T> sour
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Observable<T> fromPublisher(@NonNull Publisher<? extends T> publisher) {
+    public static <T> Observable<T> fromPublisher(@NonNull Publisher<@NonNull ? extends T> publisher) {
         Objects.requireNonNull(publisher, "publisher is null");
         return RxJavaPlugins.onAssembly(new ObservableFromPublisher<>(publisher));
     }
@@ -2831,7 +2831,7 @@ public static <T> Observable<T> just(@NonNull T item1, @NonNull T item2, @NonNul
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> merge(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
+    public static <T> Observable<T> merge(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), false, maxConcurrency, bufferSize);
     }
 
@@ -2923,7 +2923,7 @@ public static <T> Observable<T> mergeArray(int maxConcurrency, int bufferSize, @
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> merge(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> merge(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         return fromIterable(sources).flatMap((Function)Functions.identity());
     }
 
@@ -2970,7 +2970,7 @@ public static <T> Observable<T> merge(@NonNull Iterable<? extends ObservableSour
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> merge(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
+    public static <T> Observable<T> merge(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), maxConcurrency);
     }
 
@@ -3289,7 +3289,7 @@ public static <T> Observable<T> mergeArray(@NonNull ObservableSource<? extends T
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources) {
+    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true);
     }
 
@@ -3328,7 +3328,7 @@ public static <T> Observable<T> mergeDelayError(@NonNull Iterable<? extends Obse
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
+    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, int maxConcurrency, int bufferSize) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true, maxConcurrency, bufferSize);
     }
 
@@ -3405,7 +3405,7 @@ public static <T> Observable<T> mergeArrayDelayError(int maxConcurrency, int buf
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
+    public static <T> Observable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, int maxConcurrency) {
         return fromIterable(sources).flatMap((Function)Functions.identity(), true, maxConcurrency);
     }
 
@@ -4261,7 +4261,7 @@ public static <T> Observable<T> wrap(@NonNull ObservableSource<T> source) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T, R> Observable<R> zip(@NonNull Iterable<? extends ObservableSource<? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
+    public static <T, R> Observable<R> zip(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources, @NonNull Function<? super Object[], ? extends R> zipper) {
         Objects.requireNonNull(zipper, "zipper is null");
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new ObservableZip<>(null, sources, zipper, bufferSize(), false));
@@ -4322,7 +4322,7 @@ public static <T, R> Observable<R> zip(@NonNull Iterable<? extends ObservableSou
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public static <T, R> Observable<R> zip(@NonNull Iterable<? extends ObservableSource<? extends T>> sources,
+    public static <T, R> Observable<R> zip(@NonNull Iterable<@NonNull ? extends ObservableSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> zipper, boolean delayError,
             int bufferSize) {
         Objects.requireNonNull(zipper, "zipper is null");
@@ -7107,7 +7107,7 @@ public final Completable concatMapCompletableDelayError(@NonNull Function<? supe
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U> Observable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Observable<U> concatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new ObservableFlattenIterable<>(this, mapper));
     }
@@ -9310,7 +9310,7 @@ public final Completable flatMapCompletable(@NonNull Function<? super T, ? exten
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U> Observable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Observable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new ObservableFlattenIterable<>(this, mapper));
     }
@@ -9344,7 +9344,7 @@ public final <U> Observable<U> flatMapIterable(@NonNull Function<? super T, ? ex
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, V> Observable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper,
+    public final <U, V> Observable<V> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper,
             @NonNull BiFunction<? super T, ? super U, ? extends V> combiner) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(combiner, "combiner is null");
@@ -12725,7 +12725,7 @@ public final Observable<T> sorted(@NonNull Comparator<? super T> sortFunction) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Observable<T> startWithIterable(@NonNull Iterable<? extends T> items) {
+    public final Observable<T> startWithIterable(@NonNull Iterable<@NonNull ? extends T> items) {
         return concatArray(fromIterable(items), this);
     }
 
@@ -16163,7 +16163,7 @@ public final <R> Observable<R> withLatestFrom(@NonNull ObservableSource<?>[] oth
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Observable<R> withLatestFrom(@NonNull Iterable<? extends ObservableSource<?>> others, @NonNull Function<? super Object[], R> combiner) {
+    public final <R> Observable<R> withLatestFrom(@NonNull Iterable<@NonNull ? extends ObservableSource<?>> others, @NonNull Function<? super Object[], R> combiner) {
         Objects.requireNonNull(others, "others is null");
         Objects.requireNonNull(combiner, "combiner is null");
         return RxJavaPlugins.onAssembly(new ObservableWithLatestFromMany<>(this, others, combiner));
@@ -16199,7 +16199,7 @@ public final <R> Observable<R> withLatestFrom(@NonNull Iterable<? extends Observ
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U, R> Observable<R> zipWith(@NonNull Iterable<U> other, @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
+    public final <@NonNull U, R> Observable<R> zipWith(@NonNull Iterable<U> other, @NonNull BiFunction<? super T, ? super U, ? extends R> zipper) {
         Objects.requireNonNull(other, "other is null");
         Objects.requireNonNull(zipper, "zipper is null");
         return RxJavaPlugins.onAssembly(new ObservableZipIterable<>(this, other, zipper));
@@ -16853,7 +16853,7 @@ public final Stream<T> blockingStream(int capacityHint) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Observable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper) {
+    public final <@NonNull R> Observable<R> concatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper) {
         return flatMapStream(mapper);
     }
 
@@ -16900,7 +16900,7 @@ public final Stream<T> blockingStream(int capacityHint) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> Observable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper) {
+    public final <@NonNull R> Observable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new ObservableFlatMapStream<>(this, mapper));
     }
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableConverter.java b/src/main/java/io/reactivex/rxjava3/core/ObservableConverter.java
index acdde63b29..7ab3a30a74 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableConverter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableConverter.java
@@ -24,13 +24,12 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface ObservableConverter<T, R> {
+public interface ObservableConverter<@NonNull T, @NonNull R> {
     /**
      * Applies a function to the upstream {@link Observable} and returns a converted value of type {@code R}.
      *
      * @param upstream the upstream {@code Observable} instance
      * @return the converted value
      */
-    @NonNull
     R apply(@NonNull Observable<T> upstream);
 }
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableEmitter.java b/src/main/java/io/reactivex/rxjava3/core/ObservableEmitter.java
index 776d6963d9..1ce0b93687 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableEmitter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableEmitter.java
@@ -15,7 +15,7 @@
 
 import io.reactivex.rxjava3.annotations.*;
 import io.reactivex.rxjava3.disposables.Disposable;
-import io.reactivex.rxjava3.functions.Cancellable;
+import io.reactivex.rxjava3.functions.*;
 
 /**
  * Abstraction over an RxJava {@link Observer} that allows associating
@@ -47,7 +47,7 @@
  *
  * @param <T> the value type to emit
  */
-public interface ObservableEmitter<T> extends Emitter<T> {
+public interface ObservableEmitter<@NonNull T> extends Emitter<T> {
 
     /**
      * Sets a {@link Disposable} on this emitter; any previous {@code Disposable}
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableOnSubscribe.java b/src/main/java/io/reactivex/rxjava3/core/ObservableOnSubscribe.java
index bcde496462..de98fe0817 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableOnSubscribe.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableOnSubscribe.java
@@ -22,7 +22,7 @@
  * @param <T> the value type pushed
  */
 @FunctionalInterface
-public interface ObservableOnSubscribe<T> {
+public interface ObservableOnSubscribe<@NonNull T> {
 
     /**
      * Called for each {@link Observer} that subscribes.
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableOperator.java b/src/main/java/io/reactivex/rxjava3/core/ObservableOperator.java
index ff9dbc5852..749bfa1a70 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableOperator.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableOperator.java
@@ -22,7 +22,7 @@
  * @param <Upstream> the value type of the upstream
  */
 @FunctionalInterface
-public interface ObservableOperator<Downstream, Upstream> {
+public interface ObservableOperator<@NonNull Downstream, @NonNull Upstream> {
     /**
      * Applies a function to the child {@link Observer} and returns a new parent {@code Observer}.
      * @param observer the child {@code Observer} instance
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableSource.java b/src/main/java/io/reactivex/rxjava3/core/ObservableSource.java
index c2309e5b8d..89603f8e9c 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableSource.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableSource.java
@@ -22,7 +22,7 @@
  * @since 2.0
  */
 @FunctionalInterface
-public interface ObservableSource<T> {
+public interface ObservableSource<@NonNull T> {
 
     /**
      * Subscribes the given {@link Observer} to this {@link ObservableSource} instance.
diff --git a/src/main/java/io/reactivex/rxjava3/core/ObservableTransformer.java b/src/main/java/io/reactivex/rxjava3/core/ObservableTransformer.java
index 18ce5e02c9..e6686e2e97 100644
--- a/src/main/java/io/reactivex/rxjava3/core/ObservableTransformer.java
+++ b/src/main/java/io/reactivex/rxjava3/core/ObservableTransformer.java
@@ -22,7 +22,7 @@
  * @param <Downstream> the downstream value type
  */
 @FunctionalInterface
-public interface ObservableTransformer<Upstream, Downstream> {
+public interface ObservableTransformer<@NonNull Upstream, @NonNull Downstream> {
     /**
      * Applies a function to the upstream {@link Observable} and returns an {@link ObservableSource} with
      * optionally different element type.
diff --git a/src/main/java/io/reactivex/rxjava3/core/Observer.java b/src/main/java/io/reactivex/rxjava3/core/Observer.java
index de02f8ac88..dd4fb58711 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Observer.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Observer.java
@@ -73,7 +73,7 @@
  * @param <T>
  *          the type of item the Observer expects to observe
  */
-public interface Observer<T> {
+public interface Observer<@NonNull T> {
 
     /**
      * Provides the {@link Observer} with the means of cancelling (disposing) the
diff --git a/src/main/java/io/reactivex/rxjava3/core/Single.java b/src/main/java/io/reactivex/rxjava3/core/Single.java
index a1fae2e6fc..b5dde711ba 100644
--- a/src/main/java/io/reactivex/rxjava3/core/Single.java
+++ b/src/main/java/io/reactivex/rxjava3/core/Single.java
@@ -113,7 +113,7 @@
  * @since 2.0
  * @see io.reactivex.rxjava3.observers.DisposableSingleObserver
  */
-public abstract class Single<T> implements SingleSource<T> {
+public abstract class Single<@NonNull T> implements SingleSource<T> {
 
     /**
      * Runs multiple {@link SingleSource}s and signals the events of the first one that signals (disposing
@@ -134,7 +134,7 @@ public abstract class Single<T> implements SingleSource<T> {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Single<T> amb(@NonNull Iterable<? extends SingleSource<? extends T>> sources) {
+    public static <T> Single<T> amb(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new SingleAmb<>(null, sources));
     }
@@ -193,7 +193,7 @@ public static <T> Single<T> ambArray(@NonNull SingleSource<? extends T>... sourc
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <T> Flowable<T> concat(@NonNull Iterable<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources) {
         return concat(Flowable.fromIterable(sources));
     }
 
@@ -243,7 +243,7 @@ public static <T> Observable<T> concat(@NonNull ObservableSource<? extends Singl
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends SingleSource<? extends T>> sources) {
         return concat(sources, 2);
     }
 
@@ -272,7 +272,7 @@ public static <T> Flowable<T> concat(@NonNull Publisher<? extends SingleSource<?
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    public static <T> Flowable<T> concat(@NonNull Publisher<? extends SingleSource<? extends T>> sources, int prefetch) {
+    public static <T> Flowable<T> concat(@NonNull Publisher<@NonNull ? extends SingleSource<? extends T>> sources, int prefetch) {
         Objects.requireNonNull(sources, "sources is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new FlowableConcatMapPublisher(sources, SingleInternalHelper.toFlowable(), prefetch, ErrorMode.IMMEDIATE));
@@ -465,7 +465,7 @@ public static <T> Flowable<T> concatArrayEager(@NonNull SingleSource<? extends T
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Publisher<@NonNull ? extends SingleSource<? extends T>> sources) {
         return Flowable.fromPublisher(sources).concatMapEager(SingleInternalHelper.toFlowable());
     }
 
@@ -492,7 +492,7 @@ public static <T> Flowable<T> concatEager(@NonNull Publisher<? extends SingleSou
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> concatEager(@NonNull Iterable<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> concatEager(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources) {
         return Flowable.fromIterable(sources).concatMapEager(SingleInternalHelper.toFlowable());
     }
 
@@ -765,7 +765,7 @@ public static <T> Single<T> error(@NonNull Throwable exception) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Single<T> fromPublisher(@NonNull Publisher<? extends T> publisher) {
+    public static <T> Single<T> fromPublisher(@NonNull Publisher<@NonNull ? extends T> publisher) {
         Objects.requireNonNull(publisher, "publisher is null");
         return RxJavaPlugins.onAssembly(new SingleFromPublisher<>(publisher));
     }
@@ -898,7 +898,7 @@ public static <T> Single<T> fromObservable(@NonNull ObservableSource<? extends T
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> merge(@NonNull Iterable<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources) {
         return merge(Flowable.fromIterable(sources));
     }
 
@@ -938,7 +938,7 @@ public static <T> Flowable<T> merge(@NonNull Iterable<? extends SingleSource<? e
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    public static <T> Flowable<T> merge(@NonNull Publisher<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> merge(@NonNull Publisher<@NonNull ? extends SingleSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, SingleInternalHelper.toFlowable(), false, Integer.MAX_VALUE, Flowable.bufferSize()));
     }
@@ -1155,7 +1155,7 @@ public static <T> Flowable<T> merge(
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources) {
         return mergeDelayError(Flowable.fromIterable(sources));
     }
 
@@ -1183,7 +1183,7 @@ public static <T> Flowable<T> mergeDelayError(@NonNull Iterable<? extends Single
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @SuppressWarnings({ "unchecked", "rawtypes" })
-    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<? extends SingleSource<? extends T>> sources) {
+    public static <T> Flowable<T> mergeDelayError(@NonNull Publisher<@NonNull ? extends SingleSource<? extends T>> sources) {
         Objects.requireNonNull(sources, "sources is null");
         return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, SingleInternalHelper.toFlowable(), true, Integer.MAX_VALUE, Flowable.bufferSize()));
     }
@@ -1564,7 +1564,7 @@ public static <T> Single<T> wrap(@NonNull SingleSource<T> source) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public static <T, R> Single<R> zip(@NonNull Iterable<? extends SingleSource<? extends T>> sources,
+    public static <T, R> Single<R> zip(@NonNull Iterable<@NonNull ? extends SingleSource<? extends T>> sources,
             @NonNull Function<? super Object[], ? extends R> zipper) {
         Objects.requireNonNull(zipper, "zipper is null");
         Objects.requireNonNull(sources, "sources is null");
@@ -2654,7 +2654,7 @@ public final Single<T> doOnSuccess(@NonNull Consumer<? super T> onSuccess) {
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final Single<T> doOnEvent(@NonNull BiConsumer<? super T, ? super Throwable> onEvent) {
+    public final Single<T> doOnEvent(@NonNull BiConsumer<@Nullable ? super T, @Nullable ? super Throwable> onEvent) {
         Objects.requireNonNull(onEvent, "onEvent is null");
         return RxJavaPlugins.onAssembly(new SingleDoOnEvent<>(this, onEvent));
     }
@@ -2806,7 +2806,7 @@ public final <R> Maybe<R> flatMapMaybe(@NonNull Function<? super T, ? extends Ma
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> Flowable<R> flatMapPublisher(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> Flowable<R> flatMapPublisher(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlatMapPublisher<>(this, mapper));
     }
@@ -2837,7 +2837,7 @@ public final <R> Flowable<R> flatMapPublisher(@NonNull Function<? super T, ? ext
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlatMapIterableFlowable<>(this, mapper));
     }
@@ -2865,7 +2865,7 @@ public final <U> Flowable<U> flattenAsFlowable(@NonNull Function<? super T, ? ex
     @CheckReturnValue
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <@NonNull U> Observable<U> flattenAsObservable(@NonNull Function<@NonNull ? super T, @NonNull ? extends Iterable<? extends U>> mapper) {
+    public final <@NonNull U> Observable<U> flattenAsObservable(@NonNull Function<@NonNull ? super T, @NonNull ? extends Iterable<@NonNull ? extends U>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlatMapIterableObservable<>(this, mapper));
     }
@@ -3465,7 +3465,7 @@ public final Flowable<T> repeat(long times) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<?>> handler) {
+    public final Flowable<T> repeatWhen(@NonNull Function<? super Flowable<Object>, ? extends Publisher<@NonNull ?>> handler) {
         return toFlowable().repeatWhen(handler);
     }
 
@@ -3649,7 +3649,7 @@ public final Single<T> retry(@NonNull Predicate<? super Throwable> predicate) {
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final Single<T> retryWhen(@NonNull Function<? super Flowable<Throwable>, ? extends Publisher<?>> handler) {
+    public final Single<T> retryWhen(@NonNull Function<? super Flowable<Throwable>, ? extends Publisher<@NonNull ?>> handler) {
         return toSingle(toFlowable().retryWhen(handler));
     }
 
@@ -4410,7 +4410,7 @@ public final CompletionStage<T> toCompletionStage() {
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
     @NonNull
-    public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T, ? extends Stream<? extends R>> mapper) {
+    public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlattenStreamAsFlowable<>(this, mapper));
     }
@@ -4451,7 +4451,7 @@ public final <R> Flowable<R> flattenStreamAsFlowable(@NonNull Function<? super T
     @CheckReturnValue
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <R> Observable<R> flattenStreamAsObservable(@NonNull Function<? super T, ? extends Stream<? extends R>> mapper) {
+    public final <R> Observable<R> flattenStreamAsObservable(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new SingleFlattenStreamAsObservable<>(this, mapper));
     }
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleConverter.java b/src/main/java/io/reactivex/rxjava3/core/SingleConverter.java
index eb100b6c87..ce3a446452 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleConverter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleConverter.java
@@ -24,13 +24,12 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface SingleConverter<T, R> {
+public interface SingleConverter<@NonNull T, @NonNull R> {
     /**
      * Applies a function to the upstream {@link Single} and returns a converted value of type {@code R}.
      *
      * @param upstream the upstream {@code Single} instance
      * @return the converted value
      */
-    @NonNull
     R apply(@NonNull Single<T> upstream);
 }
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleEmitter.java b/src/main/java/io/reactivex/rxjava3/core/SingleEmitter.java
index bb3768243d..c8d0a79ec3 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleEmitter.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleEmitter.java
@@ -15,7 +15,7 @@
 
 import io.reactivex.rxjava3.annotations.*;
 import io.reactivex.rxjava3.disposables.Disposable;
-import io.reactivex.rxjava3.functions.Cancellable;
+import io.reactivex.rxjava3.functions.*;
 
 /**
  * Abstraction over an RxJava {@link SingleObserver} that allows associating
@@ -47,7 +47,7 @@
  *
  * @param <T> the value type to emit
  */
-public interface SingleEmitter<T> {
+public interface SingleEmitter<@NonNull T> {
 
     /**
      * Signal a success value.
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleObserver.java b/src/main/java/io/reactivex/rxjava3/core/SingleObserver.java
index d2d788d38f..281c15e531 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleObserver.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleObserver.java
@@ -50,7 +50,7 @@
  *          the type of item the SingleObserver expects to observe
  * @since 2.0
  */
-public interface SingleObserver<T> {
+public interface SingleObserver<@NonNull T> {
 
     /**
      * Provides the {@link SingleObserver} with the means of cancelling (disposing) the
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleOnSubscribe.java b/src/main/java/io/reactivex/rxjava3/core/SingleOnSubscribe.java
index 7a6a5adf68..14ff5e1f97 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleOnSubscribe.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleOnSubscribe.java
@@ -22,7 +22,7 @@
  * @param <T> the value type pushed
  */
 @FunctionalInterface
-public interface SingleOnSubscribe<T> {
+public interface SingleOnSubscribe<@NonNull T> {
 
     /**
      * Called for each {@link SingleObserver} that subscribes.
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleOperator.java b/src/main/java/io/reactivex/rxjava3/core/SingleOperator.java
index de2f38f23d..f3975b3a7f 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleOperator.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleOperator.java
@@ -22,7 +22,7 @@
  * @param <Upstream> the value type of the upstream
  */
 @FunctionalInterface
-public interface SingleOperator<Downstream, Upstream> {
+public interface SingleOperator<@NonNull Downstream, @NonNull Upstream> {
     /**
      * Applies a function to the child {@link SingleObserver} and returns a new parent {@code SingleObserver}.
      * @param observer the child {@code SingleObserver} instance
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleSource.java b/src/main/java/io/reactivex/rxjava3/core/SingleSource.java
index b4c923905d..bbeeaac40b 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleSource.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleSource.java
@@ -25,7 +25,7 @@
  * @since 2.0
  */
 @FunctionalInterface
-public interface SingleSource<T> {
+public interface SingleSource<@NonNull T> {
 
     /**
      * Subscribes the given {@link SingleObserver} to this {@link SingleSource} instance.
diff --git a/src/main/java/io/reactivex/rxjava3/core/SingleTransformer.java b/src/main/java/io/reactivex/rxjava3/core/SingleTransformer.java
index 1f0d478a0e..f3edca3430 100644
--- a/src/main/java/io/reactivex/rxjava3/core/SingleTransformer.java
+++ b/src/main/java/io/reactivex/rxjava3/core/SingleTransformer.java
@@ -22,7 +22,7 @@
  * @param <Downstream> the downstream value type
  */
 @FunctionalInterface
-public interface SingleTransformer<Upstream, Downstream> {
+public interface SingleTransformer<@NonNull Upstream, @NonNull Downstream> {
     /**
      * Applies a function to the upstream {@link Single} and returns a {@link SingleSource} with
      * optionally different element type.
diff --git a/src/main/java/io/reactivex/rxjava3/functions/BiConsumer.java b/src/main/java/io/reactivex/rxjava3/functions/BiConsumer.java
index 7fa60ef4c7..85ce3dbd17 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/BiConsumer.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/BiConsumer.java
@@ -13,13 +13,15 @@
 
 package io.reactivex.rxjava3.functions;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * A functional interface (callback) that accepts two values (of possibly different types).
  * @param <T1> the first value type
  * @param <T2> the second value type
  */
 @FunctionalInterface
-public interface BiConsumer<T1, T2> {
+public interface BiConsumer<@NonNull T1, @NonNull T2> {
 
     /**
      * Performs an operation on the given values.
diff --git a/src/main/java/io/reactivex/rxjava3/functions/BiFunction.java b/src/main/java/io/reactivex/rxjava3/functions/BiFunction.java
index 174cc3c6d9..0724ef5bd1 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/BiFunction.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/BiFunction.java
@@ -22,7 +22,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface BiFunction<T1, T2, R> {
+public interface BiFunction<@NonNull T1, @NonNull T2, @NonNull R> {
 
     /**
      * Calculate a value based on the input values.
@@ -31,6 +31,5 @@ public interface BiFunction<T1, T2, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2) throws Throwable;
+    R apply(T1 t1, T2 t2) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/BiPredicate.java b/src/main/java/io/reactivex/rxjava3/functions/BiPredicate.java
index fc41682ef5..393ec86ab7 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/BiPredicate.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/BiPredicate.java
@@ -21,7 +21,7 @@
  * @param <T2> the second value
  */
 @FunctionalInterface
-public interface BiPredicate<T1, T2> {
+public interface BiPredicate<@NonNull T1, @NonNull T2> {
 
     /**
      * Test the given input values and return a boolean.
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Consumer.java b/src/main/java/io/reactivex/rxjava3/functions/Consumer.java
index 788622c170..bf245bdcb7 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Consumer.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Consumer.java
@@ -13,12 +13,14 @@
 
 package io.reactivex.rxjava3.functions;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * A functional interface (callback) that accepts a single value.
  * @param <T> the value type
  */
 @FunctionalInterface
-public interface Consumer<T> {
+public interface Consumer<@NonNull T> {
     /**
      * Consume the given value.
      * @param t the value
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function.java b/src/main/java/io/reactivex/rxjava3/functions/Function.java
index d81a2dec52..0f8b2fe39a 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function.java
@@ -23,12 +23,12 @@
  * @param <R> the output value type
  */
 @FunctionalInterface
-public interface Function<T, R> {
+public interface Function<@NonNull T, @NonNull R> {
     /**
      * Apply some calculation to the input value and return some other value.
      * @param t the input value
      * @return the output value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    R apply(@NonNull T t) throws Throwable;
+    R apply(T t) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function3.java b/src/main/java/io/reactivex/rxjava3/functions/Function3.java
index cdc65112e7..fb1fe5aa76 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function3.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function3.java
@@ -23,7 +23,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function3<T1, T2, T3, R> {
+public interface Function3<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -32,6 +32,5 @@ public interface Function3<T1, T2, T3, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function4.java b/src/main/java/io/reactivex/rxjava3/functions/Function4.java
index 84c3ab1449..9c0af4737d 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function4.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function4.java
@@ -24,7 +24,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function4<T1, T2, T3, T4, R> {
+public interface Function4<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -34,6 +34,5 @@ public interface Function4<T1, T2, T3, T4, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function5.java b/src/main/java/io/reactivex/rxjava3/functions/Function5.java
index 77f2ff7220..fddaa28152 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function5.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function5.java
@@ -25,7 +25,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function5<T1, T2, T3, T4, T5, R> {
+public interface Function5<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull T5, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -36,6 +36,5 @@ public interface Function5<T1, T2, T3, T4, T5, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4, @NonNull T5 t5) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function6.java b/src/main/java/io/reactivex/rxjava3/functions/Function6.java
index 50c25f3df9..1f6ad10d20 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function6.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function6.java
@@ -26,7 +26,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function6<T1, T2, T3, T4, T5, T6, R> {
+public interface Function6<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull T5, @NonNull T6, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -38,6 +38,5 @@ public interface Function6<T1, T2, T3, T4, T5, T6, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4, @NonNull T5 t5, @NonNull T6 t6) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function7.java b/src/main/java/io/reactivex/rxjava3/functions/Function7.java
index 613800a4c1..39a6b26916 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function7.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function7.java
@@ -27,7 +27,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function7<T1, T2, T3, T4, T5, T6, T7, R> {
+public interface Function7<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull T5, @NonNull T6, @NonNull T7, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -40,6 +40,5 @@ public interface Function7<T1, T2, T3, T4, T5, T6, T7, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4, @NonNull T5 t5, @NonNull T6 t6, @NonNull T7 t7) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function8.java b/src/main/java/io/reactivex/rxjava3/functions/Function8.java
index 2fda54ea40..907c68cdfe 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function8.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function8.java
@@ -28,7 +28,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function8<T1, T2, T3, T4, T5, T6, T7, T8, R> {
+public interface Function8<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull T5, @NonNull T6, @NonNull T7, @NonNull T8, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -42,6 +42,5 @@ public interface Function8<T1, T2, T3, T4, T5, T6, T7, T8, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4, @NonNull T5 t5, @NonNull T6 t6, @NonNull T7 t7, @NonNull T8 t8) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7, T8 t8) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Function9.java b/src/main/java/io/reactivex/rxjava3/functions/Function9.java
index 3eb0779e30..a7f7518456 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Function9.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Function9.java
@@ -29,7 +29,7 @@
  * @param <R> the result type
  */
 @FunctionalInterface
-public interface Function9<T1, T2, T3, T4, T5, T6, T7, T8, T9, R> {
+public interface Function9<@NonNull T1, @NonNull T2, @NonNull T3, @NonNull T4, @NonNull T5, @NonNull T6, @NonNull T7, @NonNull T8, @NonNull T9, @NonNull R> {
     /**
      * Calculate a value based on the input values.
      * @param t1 the first value
@@ -44,6 +44,5 @@ public interface Function9<T1, T2, T3, T4, T5, T6, T7, T8, T9, R> {
      * @return the result value
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
-    R apply(@NonNull T1 t1, @NonNull T2 t2, @NonNull T3 t3, @NonNull T4 t4, @NonNull T5 t5, @NonNull T6 t6, @NonNull T7 t7, @NonNull T8 t8, @NonNull T9 t9) throws Throwable;
+    R apply(T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7, T8 t8, T9 t9) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/IntFunction.java b/src/main/java/io/reactivex/rxjava3/functions/IntFunction.java
index e01cc13ab5..9859bfd3c6 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/IntFunction.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/IntFunction.java
@@ -19,13 +19,12 @@
  * @param <T> the returned value type
  */
 @FunctionalInterface
-public interface IntFunction<T> {
+public interface IntFunction<@NonNull T> {
     /**
      * Calculates a value based on a primitive integer input.
      * @param i the input value
      * @return the result Object
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    @NonNull
     T apply(int i) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Predicate.java b/src/main/java/io/reactivex/rxjava3/functions/Predicate.java
index 99450f865b..550a365e60 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Predicate.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Predicate.java
@@ -20,12 +20,12 @@
  * @param <T> the first value
  */
 @FunctionalInterface
-public interface Predicate<T> {
+public interface Predicate<@NonNull T> {
     /**
      * Test the given input value and return a boolean.
      * @param t the value
      * @return the boolean result
      * @throws Throwable if the implementation wishes to throw any type of exception
      */
-    boolean test(@NonNull T t) throws Throwable;
+    boolean test(T t) throws Throwable;
 }
diff --git a/src/main/java/io/reactivex/rxjava3/functions/Supplier.java b/src/main/java/io/reactivex/rxjava3/functions/Supplier.java
index af5052ab83..5a6245f05d 100644
--- a/src/main/java/io/reactivex/rxjava3/functions/Supplier.java
+++ b/src/main/java/io/reactivex/rxjava3/functions/Supplier.java
@@ -13,6 +13,8 @@
 
 package io.reactivex.rxjava3.functions;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * A functional interface (callback) that provides a single value or
  * throws an exception.
@@ -23,7 +25,7 @@
  * @since 3.0.0
  */
 @FunctionalInterface
-public interface Supplier<T> {
+public interface Supplier<@NonNull T> {
 
     /**
      * Produces a value or throws an exception.
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/ConditionalSubscriber.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/ConditionalSubscriber.java
index 2b4fe68be1..9db35aed02 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/ConditionalSubscriber.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/ConditionalSubscriber.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.FlowableSubscriber;
 
 /**
@@ -25,12 +26,12 @@
  *
  * @param <T> the value type
  */
-public interface ConditionalSubscriber<T> extends FlowableSubscriber<T> {
+public interface ConditionalSubscriber<@NonNull T> extends FlowableSubscriber<T> {
     /**
      * Conditionally takes the value.
      * @param t the value to deliver
      * @return true if the value has been accepted, false if the value has been rejected
      * and the next value can be sent immediately
      */
-    boolean tryOnNext(T t);
+    boolean tryOnNext(@NonNull T t);
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToFlowable.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToFlowable.java
index 2b7bb614e7..6ad462c706 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToFlowable.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToFlowable.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.Flowable;
 
 /**
@@ -32,12 +33,13 @@
  *
  * @param <T> the value type
  */
-public interface FuseToFlowable<T> {
+public interface FuseToFlowable<@NonNull T> {
 
     /**
      * Returns a (direct) Flowable for the operator.
      * <p>The implementation should handle the necessary RxJavaPlugins wrapping.
      * @return the Flowable instance
      */
+    @NonNull
     Flowable<T> fuseToFlowable();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToMaybe.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToMaybe.java
index c2db8c7de6..572255a7bc 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToMaybe.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToMaybe.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.Maybe;
 
 /**
@@ -32,12 +33,13 @@
  *
  * @param <T> the value type
  */
-public interface FuseToMaybe<T> {
+public interface FuseToMaybe<@NonNull T> {
 
     /**
      * Returns a (direct) Maybe for the operator.
      * <p>The implementation should handle the necessary RxJavaPlugins wrapping.
      * @return the Maybe instance
      */
+    @NonNull
     Maybe<T> fuseToMaybe();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToObservable.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToObservable.java
index 8488ccf6e8..567d3c9a7c 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToObservable.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/FuseToObservable.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.Observable;
 
 /**
@@ -32,12 +33,13 @@
  *
  * @param <T> the value type
  */
-public interface FuseToObservable<T> {
+public interface FuseToObservable<@NonNull T> {
 
     /**
      * Returns a (direct) Observable for the operator.
      * <p>The implementation should handle the necessary RxJavaPlugins wrapping.
      * @return the Observable instance
      */
+    @NonNull
     Observable<T> fuseToObservable();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamCompletableSource.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamCompletableSource.java
index 38f199b9dc..cb6c18edd5 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamCompletableSource.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamCompletableSource.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.CompletableSource;
 
 /**
@@ -25,5 +26,6 @@ public interface HasUpstreamCompletableSource {
      * <p>Allows discovering the chain of observables.
      * @return the source CompletableSource
      */
+    @NonNull
     CompletableSource source();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamMaybeSource.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamMaybeSource.java
index 0a7d36ed86..6f4fcd9085 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamMaybeSource.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamMaybeSource.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.MaybeSource;
 
 /**
@@ -21,11 +22,12 @@
  *
  * @param <T> the value type
  */
-public interface HasUpstreamMaybeSource<T> {
+public interface HasUpstreamMaybeSource<@NonNull T> {
     /**
      * Returns the upstream source of this Maybe.
      * <p>Allows discovering the chain of observables.
      * @return the source MaybeSource
      */
+    @NonNull
     MaybeSource<T> source();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamObservableSource.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamObservableSource.java
index 0ab946c4c0..8bd340a6c0 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamObservableSource.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamObservableSource.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.ObservableSource;
 
 /**
@@ -21,11 +22,12 @@
  *
  * @param <T> the value type
  */
-public interface HasUpstreamObservableSource<T> {
+public interface HasUpstreamObservableSource<@NonNull T> {
     /**
      * Returns the upstream source of this Observable.
      * <p>Allows discovering the chain of observables.
      * @return the source ObservableSource
      */
+    @NonNull
     ObservableSource<T> source();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamPublisher.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamPublisher.java
index 9afa5ce9e0..a412b37e1d 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamPublisher.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamPublisher.java
@@ -15,13 +15,15 @@
 
 import org.reactivestreams.Publisher;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * Interface indicating the implementor has an upstream Publisher-like source available
  * via {@link #source()} method.
  *
  * @param <T> the value type
  */
-public interface HasUpstreamPublisher<T> {
+public interface HasUpstreamPublisher<@NonNull T> {
     /**
      * Returns the source Publisher.
      * <p>
@@ -29,5 +31,6 @@ public interface HasUpstreamPublisher<T> {
      * graph of sequences.
      * @return the source Publisher
      */
+    @NonNull
     Publisher<T> source();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamSingleSource.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamSingleSource.java
index db94a572e1..dfab10fd9e 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamSingleSource.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/HasUpstreamSingleSource.java
@@ -13,6 +13,7 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.core.SingleSource;
 
 /**
@@ -21,11 +22,12 @@
  *
  * @param <T> the value type
  */
-public interface HasUpstreamSingleSource<T> {
+public interface HasUpstreamSingleSource<@NonNull T> {
     /**
      * Returns the upstream source of this Single.
      * <p>Allows discovering the chain of observables.
      * @return the source SingleSource
      */
+    @NonNull
     SingleSource<T> source();
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueDisposable.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueDisposable.java
index 2becb58d43..74124d918c 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueDisposable.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueDisposable.java
@@ -14,6 +14,7 @@
 
 import java.util.Queue;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.disposables.Disposable;
 
 /**
@@ -51,5 +52,5 @@
  * </ul>
  * @param <T> the value type transmitted through the queue
  */
-public interface QueueDisposable<T> extends QueueFuseable<T>, Disposable {
+public interface QueueDisposable<@NonNull T> extends QueueFuseable<T>, Disposable {
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueFuseable.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueFuseable.java
index fadc824cc7..71b93a75ad 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueFuseable.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueFuseable.java
@@ -13,11 +13,13 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * Represents a SimpleQueue plus the means and constants for requesting a fusion mode.
  * @param <T> the value type returned by the SimpleQueue.poll()
  */
-public interface QueueFuseable<T> extends SimpleQueue<T> {
+public interface QueueFuseable<@NonNull T> extends SimpleQueue<T> {
     /**
      * Returned by the {@link #requestFusion(int)} if the upstream doesn't support
      * the requested mode.
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueSubscription.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueSubscription.java
index 87599a6e40..923589377c 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueSubscription.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/QueueSubscription.java
@@ -16,6 +16,8 @@
 
 import org.reactivestreams.Subscription;
 
+import io.reactivex.rxjava3.annotations.NonNull;
+
 /**
  * An interface extending Queue and Subscription and allows negotiating
  * the fusion mode between subsequent operators  of the {@code Flowable} base reactive type.
@@ -53,5 +55,5 @@
  * </ul>
  * @param <T> the value type transmitted through the queue
  */
-public interface QueueSubscription<T> extends QueueFuseable<T>, Subscription {
+public interface QueueSubscription<@NonNull T> extends QueueFuseable<T>, Subscription {
 }
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/ScalarSupplier.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/ScalarSupplier.java
index fc0d12323f..eda6086f87 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/ScalarSupplier.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/ScalarSupplier.java
@@ -12,6 +12,7 @@
  */
 package io.reactivex.rxjava3.internal.fuseable;
 
+import io.reactivex.rxjava3.annotations.NonNull;
 import io.reactivex.rxjava3.functions.Supplier;
 
 /**
@@ -30,7 +31,7 @@
  * @param <T> the scalar value type held by the implementing reactive type
  */
 @FunctionalInterface
-public interface ScalarSupplier<T> extends Supplier<T> {
+public interface ScalarSupplier<@NonNull T> extends Supplier<T> {
 
     // overridden to remove the throws Throwable
     @Override
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimplePlainQueue.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimplePlainQueue.java
index 3708580270..c3122038c1 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimplePlainQueue.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimplePlainQueue.java
@@ -13,14 +13,14 @@
 
 package io.reactivex.rxjava3.internal.fuseable;
 
-import io.reactivex.rxjava3.annotations.Nullable;
+import io.reactivex.rxjava3.annotations.*;
 
 /**
  * Override of the SimpleQueue interface with no throws Exception on poll().
  *
  * @param <T> the value type to offer and poll, not null
  */
-public interface SimplePlainQueue<T> extends SimpleQueue<T> {
+public interface SimplePlainQueue<@NonNull T> extends SimpleQueue<T> {
 
     @Nullable
     @Override
diff --git a/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimpleQueue.java b/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimpleQueue.java
index 29af5299d8..49d893031b 100644
--- a/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimpleQueue.java
+++ b/src/main/java/io/reactivex/rxjava3/internal/fuseable/SimpleQueue.java
@@ -20,7 +20,7 @@
  *
  * @param <T> the value type to offer and poll, not null
  */
-public interface SimpleQueue<T> {
+public interface SimpleQueue<@NonNull T> {
 
     /**
      * Atomically enqueue a single.
diff --git a/src/main/java/io/reactivex/rxjava3/parallel/ParallelFlowable.java b/src/main/java/io/reactivex/rxjava3/parallel/ParallelFlowable.java
index 17d22690ad..0fb07bac37 100644
--- a/src/main/java/io/reactivex/rxjava3/parallel/ParallelFlowable.java
+++ b/src/main/java/io/reactivex/rxjava3/parallel/ParallelFlowable.java
@@ -59,7 +59,7 @@ public abstract class ParallelFlowable<@NonNull T> {
      */
     @BackpressureSupport(BackpressureKind.SPECIAL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public abstract void subscribe(@NonNull Subscriber<? super T>[] subscribers);
+    public abstract void subscribe(@NonNull Subscriber<@NonNull ? super T>[] subscribers);
 
     /**
      * Returns the number of expected parallel {@link Subscriber}s.
@@ -77,12 +77,12 @@ public abstract class ParallelFlowable<@NonNull T> {
      * @throws NullPointerException if {@code subscribers} is {@code null}
      * @throws IllegalArgumentException if {@code subscribers.length} is different from {@link #parallelism()}
      */
-    protected final boolean validate(@NonNull Subscriber<?>[] subscribers) {
+    protected final boolean validate(@NonNull Subscriber<@NonNull ?>[] subscribers) {
         Objects.requireNonNull(subscribers, "subscribers is null");
         int p = parallelism();
         if (subscribers.length != p) {
             Throwable iae = new IllegalArgumentException("parallelism = " + p + ", subscribers = " + subscribers.length);
-            for (Subscriber<?> s : subscribers) {
+            for (Subscriber<@NonNull ?> s : subscribers) {
                 EmptySubscription.error(iae, s);
             }
             return false;
@@ -110,7 +110,7 @@ protected final boolean validate(@NonNull Subscriber<?>[] subscribers) {
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <T> ParallelFlowable<T> from(@NonNull Publisher<? extends T> source) {
+    public static <@NonNull T> ParallelFlowable<T> from(@NonNull Publisher<@NonNull ? extends T> source) {
         return from(source, Runtime.getRuntime().availableProcessors(), Flowable.bufferSize());
     }
 
@@ -135,7 +135,7 @@ public static <T> ParallelFlowable<T> from(@NonNull Publisher<? extends T> sourc
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <@NonNull T> ParallelFlowable<T> from(@NonNull Publisher<? extends T> source, int parallelism) {
+    public static <@NonNull T> ParallelFlowable<T> from(@NonNull Publisher<@NonNull ? extends T> source, int parallelism) {
         return from(source, parallelism, Flowable.bufferSize());
     }
 
@@ -164,7 +164,7 @@ public static <T> ParallelFlowable<T> from(@NonNull Publisher<? extends T> sourc
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.FULL)
-    public static <@NonNull T> ParallelFlowable<T> from(@NonNull Publisher<? extends T> source,
+    public static <@NonNull T> ParallelFlowable<T> from(@NonNull Publisher<@NonNull ? extends T> source,
             int parallelism, int prefetch) {
         Objects.requireNonNull(source, "source is null");
         ObjectHelper.verifyPositive(parallelism, "parallelism");
@@ -849,7 +849,7 @@ public final ParallelFlowable<T> doAfterNext(@NonNull Consumer<? super T> onAfte
     @NonNull
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final ParallelFlowable<T> doOnError(@NonNull Consumer<Throwable> onError) {
+    public final ParallelFlowable<T> doOnError(@NonNull Consumer<? super Throwable> onError) {
         Objects.requireNonNull(onError, "onError is null");
         return RxJavaPlugins.onAssembly(new ParallelPeek<>(this,
                 Functions.emptyConsumer(),
@@ -1154,7 +1154,7 @@ public final <U> ParallelFlowable<U> compose(@NonNull ParallelTransformer<T, U>
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <R> ParallelFlowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+    public final <R> ParallelFlowable<R> flatMap(@NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return flatMap(mapper, false, Flowable.bufferSize(), Flowable.bufferSize());
     }
 
@@ -1185,7 +1185,7 @@ public final <R> ParallelFlowable<R> flatMap(@NonNull Function<? super T, ? exte
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> flatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, boolean delayError) {
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, boolean delayError) {
         return flatMap(mapper, delayError, Flowable.bufferSize(), Flowable.bufferSize());
     }
 
@@ -1219,7 +1219,7 @@ public final <R> ParallelFlowable<R> flatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> flatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper, boolean delayError, int maxConcurrency) {
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper, boolean delayError, int maxConcurrency) {
         return flatMap(mapper, delayError, maxConcurrency, Flowable.bufferSize());
     }
 
@@ -1253,7 +1253,7 @@ public final <R> ParallelFlowable<R> flatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> flatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             boolean delayError, int maxConcurrency, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(maxConcurrency, "maxConcurrency");
@@ -1285,7 +1285,7 @@ public final <R> ParallelFlowable<R> flatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> concatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper) {
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper) {
         return concatMap(mapper, 2);
     }
 
@@ -1316,7 +1316,7 @@ public final <R> ParallelFlowable<R> concatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> concatMap(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
             int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -1349,7 +1349,7 @@ public final <R> ParallelFlowable<R> concatMap(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> concatMapDelayError(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
                     boolean tillTheEnd) {
         return concatMapDelayError(mapper, 2, tillTheEnd);
     }
@@ -1382,7 +1382,7 @@ public final <R> ParallelFlowable<R> concatMapDelayError(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     public final <R> ParallelFlowable<R> concatMapDelayError(
-            @NonNull Function<? super T, ? extends Publisher<? extends R>> mapper,
+            @NonNull Function<? super T, ? extends Publisher<@NonNull ? extends R>> mapper,
                     int prefetch, boolean tillTheEnd) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
@@ -1419,7 +1419,7 @@ public final <R> ParallelFlowable<R> concatMapDelayError(
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper) {
+    public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper) {
         return flatMapIterable(mapper, Flowable.bufferSize());
     }
 
@@ -1455,7 +1455,7 @@ public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T
     @NonNull
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<? extends U>> mapper, int bufferSize) {
+    public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T, ? extends Iterable<@NonNull ? extends U>> mapper, int bufferSize) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(bufferSize, "bufferSize");
         return RxJavaPlugins.onAssembly(new ParallelFlatMapIterable<>(this, mapper, bufferSize));
@@ -1486,7 +1486,7 @@ public final <U> ParallelFlowable<U> flatMapIterable(@NonNull Function<? super T
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
-    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<? extends R>> mapper) {
+    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<@NonNull ? extends R>> mapper) {
         Objects.requireNonNull(mapper, "mapper is null");
         return RxJavaPlugins.onAssembly(new ParallelMapOptional<>(this, mapper));
     }
@@ -1516,7 +1516,7 @@ public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Op
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
-    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<? extends R>> mapper, @NonNull ParallelFailureHandling errorHandler) {
+    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<@NonNull ? extends R>> mapper, @NonNull ParallelFailureHandling errorHandler) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(errorHandler, "errorHandler is null");
         return RxJavaPlugins.onAssembly(new ParallelMapTryOptional<>(this, mapper, errorHandler));
@@ -1548,7 +1548,7 @@ public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Op
     @NonNull
     @SchedulerSupport(SchedulerSupport.NONE)
     @BackpressureSupport(BackpressureKind.PASS_THROUGH)
-    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<? extends R>> mapper, @NonNull BiFunction<? super Long, ? super Throwable, ParallelFailureHandling> errorHandler) {
+    public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Optional<@NonNull ? extends R>> mapper, @NonNull BiFunction<? super Long, ? super Throwable, ParallelFailureHandling> errorHandler) {
         Objects.requireNonNull(mapper, "mapper is null");
         Objects.requireNonNull(errorHandler, "errorHandler is null");
         return RxJavaPlugins.onAssembly(new ParallelMapTryOptional<>(this, mapper, errorHandler));
@@ -1604,7 +1604,7 @@ public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Op
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> ParallelFlowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper) {
+    public final <@NonNull R> ParallelFlowable<R> flatMapStream(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper) {
         return flatMapStream(mapper, Flowable.bufferSize());
     }
 
@@ -1658,7 +1658,7 @@ public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Op
     @BackpressureSupport(BackpressureKind.FULL)
     @SchedulerSupport(SchedulerSupport.NONE)
     @NonNull
-    public final <@NonNull R> ParallelFlowable<R> flatMapStream(@NonNull Function<? super T, @NonNull ? extends Stream<? extends R>> mapper, int prefetch) {
+    public final <@NonNull R> ParallelFlowable<R> flatMapStream(@NonNull Function<? super T, ? extends Stream<@NonNull ? extends R>> mapper, int prefetch) {
         Objects.requireNonNull(mapper, "mapper is null");
         ObjectHelper.verifyPositive(prefetch, "prefetch");
         return RxJavaPlugins.onAssembly(new ParallelFlatMapStream<>(this, mapper, prefetch));
@@ -1688,7 +1688,7 @@ public final <R> ParallelFlowable<R> mapOptional(@NonNull Function<? super T, Op
     @NonNull
     @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
     @SchedulerSupport(SchedulerSupport.NONE)
-    public final <A, R> Flowable<R> collect(@NonNull Collector<T, A, R> collector) {
+    public final <A, @NonNull R> Flowable<R> collect(@NonNull Collector<T, A, R> collector) {
         Objects.requireNonNull(collector, "collector is null");
         return RxJavaPlugins.onAssembly(new ParallelCollector<>(this, collector));
     }
diff --git a/src/main/java/io/reactivex/rxjava3/parallel/ParallelTransformer.java b/src/main/java/io/reactivex/rxjava3/parallel/ParallelTransformer.java
index 7e6a7734d0..a10a73ead4 100644
--- a/src/main/java/io/reactivex/rxjava3/parallel/ParallelTransformer.java
+++ b/src/main/java/io/reactivex/rxjava3/parallel/ParallelTransformer.java
@@ -23,7 +23,7 @@
  * @since 2.2
  */
 @FunctionalInterface
-public interface ParallelTransformer<Upstream, Downstream> {
+public interface ParallelTransformer<@NonNull Upstream, @NonNull Downstream> {
     /**
      * Applies a function to the upstream ParallelFlowable and returns a ParallelFlowable with
      * optionally different element type.
diff --git a/src/main/java/io/reactivex/rxjava3/plugins/RxJavaPlugins.java b/src/main/java/io/reactivex/rxjava3/plugins/RxJavaPlugins.java
index 9012e36f12..408eae8d36 100644
--- a/src/main/java/io/reactivex/rxjava3/plugins/RxJavaPlugins.java
+++ b/src/main/java/io/reactivex/rxjava3/plugins/RxJavaPlugins.java
@@ -918,7 +918,7 @@ public static void setOnSingleSubscribe(@Nullable BiFunction<? super Single, ? s
      */
     @SuppressWarnings({ "rawtypes", "unchecked" })
     @NonNull
-    public static <T> Subscriber<? super T> onSubscribe(@NonNull Flowable<T> source, @NonNull Subscriber<? super T> subscriber) {
+    public static <T> Subscriber<@NonNull ? super T> onSubscribe(@NonNull Flowable<T> source, @NonNull Subscriber<@NonNull ? super T> subscriber) {
         BiFunction<? super Flowable, ? super Subscriber, ? extends Subscriber> f = onFlowableSubscribe;
         if (f != null) {
             return apply(f, source, subscriber);
diff --git a/src/main/java/io/reactivex/rxjava3/processors/AsyncProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/AsyncProcessor.java
index 3461c146d6..8037c67ffe 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/AsyncProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/AsyncProcessor.java
@@ -150,7 +150,7 @@ public static <T> AsyncProcessor<T> create() {
     }
 
     @Override
-    public void onSubscribe(Subscription s) {
+    public void onSubscribe(@NonNull Subscription s) {
         if (subscribers.get() == TERMINATED) {
             s.cancel();
             return;
@@ -160,7 +160,7 @@ public void onSubscribe(Subscription s) {
     }
 
     @Override
-    public void onNext(T t) {
+    public void onNext(@NonNull T t) {
         ExceptionHelper.nullCheck(t, "onNext called with a null value.");
         if (subscribers.get() == TERMINATED) {
             return;
@@ -170,7 +170,7 @@ public void onNext(T t) {
 
     @SuppressWarnings("unchecked")
     @Override
-    public void onError(Throwable t) {
+    public void onError(@NonNull Throwable t) {
         ExceptionHelper.nullCheck(t, "onError called with a null Throwable.");
         if (subscribers.get() == TERMINATED) {
             RxJavaPlugins.onError(t);
@@ -228,7 +228,7 @@ public Throwable getThrowable() {
     }
 
     @Override
-    protected void subscribeActual(Subscriber<? super T> s) {
+    protected void subscribeActual(@NonNull Subscriber<@NonNull ? super T> s) {
         AsyncSubscription<T> as = new AsyncSubscription<>(s, this);
         s.onSubscribe(as);
         if (add(as)) {
@@ -341,7 +341,7 @@ static final class AsyncSubscription<T> extends DeferredScalarSubscription<T> {
 
         final AsyncProcessor<T> parent;
 
-        AsyncSubscription(Subscriber<? super T> actual, AsyncProcessor<T> parent) {
+        AsyncSubscription(Subscriber<@NonNull ? super T> actual, AsyncProcessor<T> parent) {
             super(actual);
             this.parent = parent;
         }
diff --git a/src/main/java/io/reactivex/rxjava3/processors/BehaviorProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/BehaviorProcessor.java
index 0b7e49ae2f..de5d744f3f 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/BehaviorProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/BehaviorProcessor.java
@@ -239,7 +239,7 @@ public static <T> BehaviorProcessor<T> create() {
     }
 
     @Override
-    protected void subscribeActual(@NonNull Subscriber<? super T> s) {
+    protected void subscribeActual(@NonNull Subscriber<@NonNull ? super T> s) {
         BehaviorSubscription<T> bs = new BehaviorSubscription<>(s, this);
         s.onSubscribe(bs);
         if (add(bs)) {
@@ -475,11 +475,11 @@ void setCurrent(Object o) {
         wl.unlock();
     }
 
-    static final class BehaviorSubscription<T> extends AtomicLong implements Subscription, NonThrowingPredicate<Object> {
+    static final class BehaviorSubscription<@NonNull T> extends AtomicLong implements Subscription, NonThrowingPredicate<Object> {
 
         private static final long serialVersionUID = 3293175281126227086L;
 
-        final Subscriber<? super T> downstream;
+        final Subscriber<@NonNull ? super T> downstream;
         final BehaviorProcessor<T> state;
 
         boolean next;
@@ -492,7 +492,7 @@ static final class BehaviorSubscription<T> extends AtomicLong implements Subscri
 
         long index;
 
-        BehaviorSubscription(Subscriber<? super T> actual, BehaviorProcessor<T> state) {
+        BehaviorSubscription(Subscriber<@NonNull ? super T> actual, BehaviorProcessor<T> state) {
             this.downstream = actual;
             this.state = state;
         }
diff --git a/src/main/java/io/reactivex/rxjava3/processors/FlowableProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/FlowableProcessor.java
index 80db65e652..86622298f6 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/FlowableProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/FlowableProcessor.java
@@ -26,7 +26,7 @@
  *
  * @param <T> the item value type
  */
-public abstract class FlowableProcessor<T> extends Flowable<T> implements Processor<T, T>, FlowableSubscriber<T> {
+public abstract class FlowableProcessor<@NonNull T> extends Flowable<T> implements Processor<T, T>, FlowableSubscriber<T> {
 
     /**
      * Returns true if the FlowableProcessor has subscribers.
diff --git a/src/main/java/io/reactivex/rxjava3/processors/MulticastProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/MulticastProcessor.java
index 7a6809b5d2..7ef61d7959 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/MulticastProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/MulticastProcessor.java
@@ -375,7 +375,7 @@ public Throwable getThrowable() {
     }
 
     @Override
-    protected void subscribeActual(@NonNull Subscriber<? super T> s) {
+    protected void subscribeActual(@NonNull Subscriber<@NonNull ? super T> s) {
         MulticastSubscription<T> ms = new MulticastSubscription<>(s, this);
         s.onSubscribe(ms);
         if (add(ms)) {
@@ -593,13 +593,13 @@ static final class MulticastSubscription<T> extends AtomicLong implements Subscr
 
         private static final long serialVersionUID = -363282618957264509L;
 
-        final Subscriber<? super T> downstream;
+        final Subscriber<@NonNull ? super T> downstream;
 
         final MulticastProcessor<T> parent;
 
         long emitted;
 
-        MulticastSubscription(Subscriber<? super T> actual, MulticastProcessor<T> parent) {
+        MulticastSubscription(Subscriber<@NonNull ? super T> actual, MulticastProcessor<T> parent) {
             this.downstream = actual;
             this.parent = parent;
         }
diff --git a/src/main/java/io/reactivex/rxjava3/processors/PublishProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/PublishProcessor.java
index 0a73cf1bf8..b507a2225b 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/PublishProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/PublishProcessor.java
@@ -141,7 +141,7 @@ public static <T> PublishProcessor<T> create() {
     }
 
     @Override
-    protected void subscribeActual(@NonNull Subscriber<? super T> t) {
+    protected void subscribeActual(@NonNull Subscriber<@NonNull ? super T> t) {
         PublishSubscription<T> ps = new PublishSubscription<>(t, this);
         t.onSubscribe(ps);
         if (add(ps)) {
@@ -336,11 +336,11 @@ public boolean hasComplete() {
      *
      * @param <T> the value type
      */
-    static final class PublishSubscription<T> extends AtomicLong implements Subscription {
+    static final class PublishSubscription<@NonNull T> extends AtomicLong implements Subscription {
 
         private static final long serialVersionUID = 3562861878281475070L;
         /** The actual subscriber. */
-        final Subscriber<? super T> downstream;
+        final Subscriber<@NonNull ? super T> downstream;
         /** The parent processor servicing this subscriber. */
         final PublishProcessor<T> parent;
 
@@ -349,7 +349,7 @@ static final class PublishSubscription<T> extends AtomicLong implements Subscrip
          * @param actual the actual subscriber
          * @param parent the parent PublishProcessor
          */
-        PublishSubscription(Subscriber<? super T> actual, PublishProcessor<T> parent) {
+        PublishSubscription(Subscriber<@NonNull ? super T> actual, PublishProcessor<T> parent) {
             this.downstream = actual;
             this.parent = parent;
         }
diff --git a/src/main/java/io/reactivex/rxjava3/processors/ReplayProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/ReplayProcessor.java
index 6e903e5aab..aa3402ec13 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/ReplayProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/ReplayProcessor.java
@@ -345,7 +345,7 @@ public static <T> ReplayProcessor<T> createWithTimeAndSize(long maxAge, @NonNull
     }
 
     @Override
-    protected void subscribeActual(Subscriber<? super T> s) {
+    protected void subscribeActual(Subscriber<@NonNull ? super T> s) {
         ReplaySubscription<T> rs = new ReplaySubscription<>(s, this);
         s.onSubscribe(rs);
 
@@ -615,7 +615,7 @@ interface ReplayBuffer<T> {
     static final class ReplaySubscription<T> extends AtomicInteger implements Subscription {
 
         private static final long serialVersionUID = 466549804534799122L;
-        final Subscriber<? super T> downstream;
+        final Subscriber<@NonNull ? super T> downstream;
         final ReplayProcessor<T> state;
 
         Object index;
@@ -626,7 +626,7 @@ static final class ReplaySubscription<T> extends AtomicInteger implements Subscr
 
         long emitted;
 
-        ReplaySubscription(Subscriber<? super T> actual, ReplayProcessor<T> state) {
+        ReplaySubscription(Subscriber<@NonNull ? super T> actual, ReplayProcessor<T> state) {
             this.downstream = actual;
             this.state = state;
             this.requested = new AtomicLong();
@@ -728,7 +728,7 @@ public void replay(ReplaySubscription<T> rs) {
 
             int missed = 1;
             final List<T> b = buffer;
-            final Subscriber<? super T> a = rs.downstream;
+            final Subscriber<@NonNull ? super T> a = rs.downstream;
 
             Integer indexObject = (Integer)rs.index;
             int index;
@@ -967,7 +967,7 @@ public void replay(ReplaySubscription<T> rs) {
             }
 
             int missed = 1;
-            final Subscriber<? super T> a = rs.downstream;
+            final Subscriber<@NonNull ? super T> a = rs.downstream;
 
             Node<T> index = (Node<T>)rs.index;
             if (index == null) {
@@ -1257,7 +1257,7 @@ public void replay(ReplaySubscription<T> rs) {
             }
 
             int missed = 1;
-            final Subscriber<? super T> a = rs.downstream;
+            final Subscriber<@NonNull ? super T> a = rs.downstream;
 
             TimedNode<T> index = (TimedNode<T>)rs.index;
             if (index == null) {
diff --git a/src/main/java/io/reactivex/rxjava3/processors/UnicastProcessor.java b/src/main/java/io/reactivex/rxjava3/processors/UnicastProcessor.java
index a1af942d8d..7d7e20a075 100644
--- a/src/main/java/io/reactivex/rxjava3/processors/UnicastProcessor.java
+++ b/src/main/java/io/reactivex/rxjava3/processors/UnicastProcessor.java
@@ -159,7 +159,7 @@ public final class UnicastProcessor<T> extends FlowableProcessor<T> {
 
     Throwable error;
 
-    final AtomicReference<Subscriber<? super T>> downstream;
+    final AtomicReference<Subscriber<@NonNull ? super T>> downstream;
 
     volatile boolean cancelled;
 
@@ -282,7 +282,7 @@ void doTerminate() {
         }
     }
 
-    void drainRegular(Subscriber<? super T> a) {
+    void drainRegular(Subscriber<@NonNull ? super T> a) {
         int missed = 1;
 
         final SpscLinkedArrayQueue<T> q = queue;
@@ -326,7 +326,7 @@ void drainRegular(Subscriber<? super T> a) {
         }
     }
 
-    void drainFused(Subscriber<? super T> a) {
+    void drainFused(Subscriber<@NonNull ? super T> a) {
         int missed = 1;
 
         final SpscLinkedArrayQueue<T> q = queue;
@@ -374,7 +374,7 @@ void drain() {
 
         int missed = 1;
 
-        Subscriber<? super T> a = downstream.get();
+        Subscriber<@NonNull ? super T> a = downstream.get();
         for (;;) {
             if (a != null) {
 
@@ -394,7 +394,7 @@ void drain() {
         }
     }
 
-    boolean checkTerminated(boolean failFast, boolean d, boolean empty, Subscriber<? super T> a, SpscLinkedArrayQueue<T> q) {
+    boolean checkTerminated(boolean failFast, boolean d, boolean empty, Subscriber<@NonNull ? super T> a, SpscLinkedArrayQueue<T> q) {
         if (cancelled) {
             q.clear();
             downstream.lazySet(null);
@@ -475,7 +475,7 @@ public void onComplete() {
     }
 
     @Override
-    protected void subscribeActual(Subscriber<? super T> s) {
+    protected void subscribeActual(Subscriber<@NonNull ? super T> s) {
         if (!once.get() && once.compareAndSet(false, true)) {
 
             s.onSubscribe(wip);
diff --git a/src/test/java/io/reactivex/rxjava3/validators/SourceAnnotationCheck.java b/src/test/java/io/reactivex/rxjava3/validators/SourceAnnotationCheck.java
index 6fb50a141b..ed1080023f 100644
--- a/src/test/java/io/reactivex/rxjava3/validators/SourceAnnotationCheck.java
+++ b/src/test/java/io/reactivex/rxjava3/validators/SourceAnnotationCheck.java
@@ -25,6 +25,7 @@
 import io.reactivex.rxjava3.flowables.ConnectableFlowable;
 import io.reactivex.rxjava3.observables.ConnectableObservable;
 import io.reactivex.rxjava3.parallel.ParallelFlowable;
+import io.reactivex.rxjava3.plugins.RxJavaPlugins;
 import io.reactivex.rxjava3.processors.*;
 import io.reactivex.rxjava3.schedulers.Schedulers;
 import io.reactivex.rxjava3.subjects.*;
@@ -172,6 +173,11 @@ public void checkMulticastProcessor() throws Exception {
         processFile(MulticastProcessor.class);
     }
 
+    @Test
+    public void checkRxJavaPlugins() throws Exception {
+        processFile(RxJavaPlugins.class);
+    }
+
     static void processFile(Class<?> clazz) throws Exception {
         String baseClassName = clazz.getSimpleName();
         File f = TestHelper.findSource(baseClassName, clazz.getPackage().getName());
@@ -376,6 +382,26 @@ else if (skippingDepth == 0) {
                     ;
                 }
             }
+
+            for (String typeName : TYPES_REQUIRING_NONNULL_TYPEARG) {
+                String pattern = typeName + "<?";
+                if (line.contains(pattern)) {
+                    errorCount++;
+                    errors.append("L")
+                    .append(j)
+                    .append(" : Missing @NonNull type argument annotation on ")
+                    .append(typeName)
+                    .append("\r\n")
+                    .append(" at ")
+                    .append(fullClassName)
+                    .append(".method(")
+                    .append(f.getName())
+                    .append(":")
+                    .append(j + 1)
+                    .append(")\r\n")
+                    ;
+                }
+            }
         }
 
         if (errorCount != 0) {
@@ -417,4 +443,8 @@ else if (skippingDepth == 0) {
 
             "T", "R", "U", "V"
     );
+
+    static final List<String> TYPES_REQUIRING_NONNULL_TYPEARG = Arrays.asList(
+            "Iterable", "Stream", "Publisher", "Subscriber", "Processor"
+    );
 }