IDL: Use Nullable for union type return value

Source/bindings/templates/methods.cpp

Index: Source/bindings/templates/methods.cpp
diff --git a/Source/bindings/templates/methods.cpp b/Source/bindings/templates/methods.cpp
index cf307e68859e6f8a5be32b7564636cd4045ddcad..714e5a6b53cc80b8e054a2b3bbc6edb231d293e5 100644
--- a/Source/bindings/templates/methods.cpp
+++ b/Source/bindings/templates/methods.cpp
@@ -296,18 +296,17 @@ if (info.Length() >= 2 && listener && !impl->toNode())
 
 {######################################}
 {% macro union_type_method_call_and_set_return_value(method) %}
-{% for cpp_type in method.cpp_type %}
-bool result{{loop.index0}}Enabled = false;
-{{cpp_type}} result{{loop.index0}};
+{% for argument in method.union_arguments %}
+{{argument.cpp_type}} {{argument.cpp_value}};
 {% endfor %}
 {{method.cpp_value}};
 {% if method.is_null_expression %}{# used by getters #}
 if ({{method.is_null_expression}})
     return;
 {% endif %}
-{% for v8_set_return_value in method.v8_set_return_value %}
-if (result{{loop.index0}}Enabled) {
-    {{v8_set_return_value}};
+{% for argument in method.union_arguments %}
+if ({{argument.null_check_value}}) {
+    {{argument.v8_set_return_value}};
     return;
 }
 {% endfor %}