Don't expect nested protobuf objects to be null

server/src/main/java/io/deephaven/server/table/ops/filter/FilterVisitor.java

@@ -9,6 +9,7 @@
 import io.deephaven.proto.backplane.grpc.MatchType;
 import io.deephaven.proto.backplane.grpc.Reference;
 import io.deephaven.proto.backplane.grpc.Value;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.List;
 
@@ -25,7 +26,7 @@ public interface FilterVisitor<R> {
 
     R onIsNull(Reference reference);
 
-    R onInvoke(String method, Value target, List<Value> argumentsList);
+    R onInvoke(String method, @Nullable Value target, List<Value> argumentsList);
 
     R onContains(Reference reference, String searchString, CaseSensitivity caseSensitivity, MatchType matchType);
 
@@ -49,7 +50,8 @@ static <R> R accept(Condition condition, FilterVisitor<R> visitor) {
                 return visitor.onIn(condition.getIn().getTarget(), condition.getIn().getCandidatesList(),
                         condition.getIn().getCaseSensitivity(), condition.getIn().getMatchType());
             case INVOKE:
-                return visitor.onInvoke(condition.getInvoke().getMethod(), condition.getInvoke().getTarget(),
+                return visitor.onInvoke(condition.getInvoke().getMethod(),
+                        condition.getInvoke().hasTarget() ? condition.getInvoke().getTarget() : null,
                         condition.getInvoke().getArgumentsList());
             case IS_NULL:
                 return visitor.onIsNull(condition.getIsNull().getReference());

server/src/main/java/io/deephaven/server/table/ops/filter/NormalizeFilterUtil.java

@@ -101,6 +101,13 @@ public static Condition doInvoke(String method, Value target, List<Value> argume
                 .build()).build();
     }
 
+    public static Condition doInvoke(String method, List<Value> argumentsList) {
+        return Condition.newBuilder().setInvoke(InvokeCondition.newBuilder()
+                .setMethod(method)
+                .addAllArguments(argumentsList)
+                .build()).build();
+    }
+
     public static Condition doContains(Reference reference, String searchString, CaseSensitivity caseSensitivity,
             MatchType matchType) {
         return Condition.newBuilder().setContains(ContainsCondition.newBuilder()

server/src/test/java/io/deephaven/server/table/ops/filter/FilterPrinterTest.java

@@ -3,9 +3,12 @@
  */
 package io.deephaven.server.table.ops.filter;
 
+import io.deephaven.proto.backplane.grpc.Condition;
 import io.deephaven.proto.backplane.grpc.Literal;
 import org.junit.Test;
 
+import static io.deephaven.server.table.ops.filter.FilterPrinter.print;
+import static io.deephaven.server.table.ops.filter.FilterTestUtils.reference;
 import static org.junit.Assert.*;
 
 public class FilterPrinterTest {
@@ -99,4 +102,17 @@ private static void rotateAndAssert(long longBits) {
     private static Literal lit(double doubleValue) {
         return Literal.newBuilder().setDoubleValue(doubleValue).build();
     }
+
+    @Test
+    public void testInvoke() {
+        Condition hello = FilterTestUtils.invoke("hello", null);
+        assertEquals("hello()", print(hello));
+        hello = FilterTestUtils.invoke("hello", reference("foo"));
+        assertEquals("foo.hello()", print(hello));
+
+        Condition helloWorld = FilterTestUtils.invoke("helloWorld", null, reference("someColumn"));
+        assertEquals("helloWorld(someColumn)", print(helloWorld));
+        helloWorld = FilterTestUtils.invoke("helloWorld", reference("foo"), reference("someColumn"));
+        assertEquals("foo.helloWorld(someColumn)", print(helloWorld));
+    }
 }

server/src/test/java/io/deephaven/server/table/ops/filter/FilterTestUtils.java

@@ -104,6 +104,9 @@ public static Condition compare(CompareCondition.CompareOperation operation, Cas
     }
 
     public static Condition invoke(String method, Value target, Value... filterDescriptors) {
+        if (target == null) {
+            return NormalizeFilterUtil.doInvoke(method, Arrays.asList(filterDescriptors));
+        }
         return NormalizeFilterUtil.doInvoke(method, target, Arrays.asList(filterDescriptors));
     }
 }