IDL: Drop redundant null check for string and wrapper type attributes

Source/bindings/templates/attributes.cpp

Index: Source/bindings/templates/attributes.cpp
diff --git a/Source/bindings/templates/attributes.cpp b/Source/bindings/templates/attributes.cpp
index 38d047971442fef63ec107232ee2ddbb9216557a..4da5ee6bccfb5b746821de8b8241f0c031be23eb 100644
--- a/Source/bindings/templates/attributes.cpp
+++ b/Source/bindings/templates/attributes.cpp
@@ -69,12 +69,8 @@ const v8::PropertyCallbackInfo<v8::Value>& info
                          attribute.cpp_value)
       | indent}}
     {% endif %}
-    {% if attribute.is_nullable %}
-    {% if attribute.is_nullable_simple %}
-    if (!{{attribute.cpp_value}}) {
-    {% else %}
+    {% if attribute.is_nullable and not attribute.is_nullable_simple %}
     if (isNull) {
-    {% endif %}
         v8SetReturnValueNull(info);
         return;
     }