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 cebccd56e0efe56a9753191c38d87a195e659b18..5734becf0f91e7eb32d471d20968b388e2cd2d37 100644
--- a/Source/bindings/templates/methods.cpp
+++ b/Source/bindings/templates/methods.cpp
@@ -297,8 +297,7 @@ 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}};
+Nullable<{{cpp_type}} > result{{loop.index0}};
 {% endfor %}
 {{method.cpp_value}};
 {% if method.is_null_expression %}{# used by getters #}
@@ -306,7 +305,7 @@ if ({{method.is_null_expression}})
     return;
 {% endif %}
 {% for v8_set_return_value in method.v8_set_return_value %}
-if (result{{loop.index0}}Enabled) {
+if (!result{{loop.index0}}.isNull()) {
     {{v8_set_return_value}};
     return;
 }