fix error in php nightly with casting null to array

OriHoch · OriHoch · commit cf429f20bf1c · 2017-07-13T10:06:58.000+03:00
diff --git a/src/Schema.php b/src/Schema.php
@@ -206,5 +206,5 @@ public function save($filename)
     }
 
     protected $descriptor;
-    protected $fieldsCache = null;
+    protected $fieldsCache = [];
 }

Original file line number	Diff line number	Diff line change
`@@ -206,5 +206,5 @@ public function save($filename)`
`206`	`206`	`}`
`207`	`207`
`208`	`208`	`protected $descriptor;`
`209`		`- protected $fieldsCache = null;`
	`209`	`+ protected $fieldsCache = [];`
`210`	`210`	`}`