IDL: Use Nullable for union type return value

Source/bindings/scripts/v8_interface.py

Index: Source/bindings/scripts/v8_interface.py
diff --git a/Source/bindings/scripts/v8_interface.py b/Source/bindings/scripts/v8_interface.py
index 549818a6cdb89e24b158e84caedeb534906ecc9e..7256bb814d1b61ca6003d5c8e6937fd664addb17 100644
--- a/Source/bindings/scripts/v8_interface.py
+++ b/Source/bindings/scripts/v8_interface.py
@@ -934,7 +934,7 @@ def interface_length(interface, constructors):
 def property_getter(getter, cpp_arguments):
     def is_null_expression(idl_type):
         if idl_type.is_union_type:
-            return ' && '.join('!result%sEnabled' % i
+            return ' && '.join('result%s.isNull()' % i
                                for i, _ in enumerate(idl_type.member_types))
         if idl_type.name == 'String':
             return 'result.isNull()'
@@ -957,6 +957,8 @@ def property_getter(getter, cpp_arguments):
 
     cpp_value = '%s(%s)' % (cpp_method_name, ', '.join(cpp_arguments))
 
+    cpp_return_value = 'result' if not idl_type.is_union_type else 'result{index}.get()'
+
     return {
         'cpp_type': idl_type.cpp_type,
         'cpp_value': cpp_value,
@@ -973,7 +975,7 @@ def property_getter(getter, cpp_arguments):
         'is_raises_exception': is_raises_exception,
         'name': cpp_name(getter),
         'union_arguments': union_arguments,
-        'v8_set_return_value': idl_type.v8_set_return_value('result', extended_attributes=extended_attributes, script_wrappable='impl', release=idl_type.release),
+        'v8_set_return_value': idl_type.v8_set_return_value(cpp_return_value, extended_attributes=extended_attributes, script_wrappable='impl', release=idl_type.release),
     }