IDL: Use Nullable for union type return value

Source/bindings/scripts/v8_methods.py

Index: Source/bindings/scripts/v8_methods.py
diff --git a/Source/bindings/scripts/v8_methods.py b/Source/bindings/scripts/v8_methods.py
index c69fcd1f3bec6af9e2d387395ce9e368fa0ed1a7..9d35b403bf5c3f27d22ef6b4e03ffe13e33bebe3 100644
--- a/Source/bindings/scripts/v8_methods.py
+++ b/Source/bindings/scripts/v8_methods.py
@@ -402,10 +402,9 @@ def property_attributes(method):
 
 
 def union_arguments(idl_type):
-    """Return list of ['result0Enabled', 'result0', 'result1Enabled', ...] for union types, for use in setting return value"""
-    return [arg
-            for i in range(len(idl_type.member_types))
-            for arg in ['result%sEnabled' % i, 'result%s' % i]]
+    """Return list of ['result0', 'result1', ...] for union types, for use in setting return value"""
+    return ['result%d' % i
+            for i in range(len(idl_type.member_types))]
 
 
 def argument_default_cpp_value(argument):