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

Source/bindings/templates/attributes.cpp

 {##############################################################################}
 {% macro attribute_getter(attribute, world_suffix) %}
 {% filter conditional(attribute.conditional_string) %}
 static void {{attribute.name}}AttributeGetter{{world_suffix}}(
 {%- if attribute.is_expose_js_accessors %}
 const v8::FunctionCallbackInfo<v8::Value>& info
 {%- else %}
 const v8::PropertyCallbackInfo<v8::Value>& info
 {%- endif %})
 {
@@ skipping 51 matching lines @@
         exceptionState.throwIfNeeded();
         return;
     }
     {% endif %}
     {% if attribute.reflect_only %}
     {{release_only_check(attribute.reflect_only, attribute.reflect_missing,
                          attribute.reflect_invalid, attribute.reflect_empty,
                          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;
     }
     {% endif %}
     {% if attribute.cached_attribute_validation_method %}
     V8HiddenValue::setHiddenValue(info.GetIsolate(), holder, propertyName, {{attribute.cpp_value_to_v8_value}});
     {% endif %}
     {# v8SetReturnValue #}
     {% if attribute.is_keep_alive_for_gc %}
     if ({{attribute.cpp_value}} && DOMDataStore::setReturnValueFromWrapper{{world_suffix}}<{{attribute.v8_type}}>(info.GetReturnValue(), {{attribute.cpp_value}}.get()))
@@ skipping 243 matching lines @@
     {% endif %}
     {% if attribute.has_custom_setter %}
     {{v8_class}}::{{attribute.name}}AttributeSetterCustom(v8Value, info);
     {% else %}
     {{cpp_class}}V8Internal::{{attribute.name}}AttributeSetter{{world_suffix}}(v8Value, info);
     {% endif %}
     TRACE_EVENT_SET_SAMPLING_STATE("v8", "V8Execution");
 }
 {% endfilter %}
 {% endmacro %}