contract nulls are compatible with array return types (IDEA-137323)

java/java-tests/testData/inspection/dataFlow/contractCheck/ReturnPrimitiveArray.java

@@ -0,0 +1,10 @@
+import org.jetbrains.annotations.Contract;
+
+class Zoo {
+  @Contract( "null->null" )
+  static byte[] bar( String s )
+  {
+    if ( s == null )
+      return null;
+    return new byte[0];
+  }}