final protected function getCompositeWidget($key)
    {
        $this->confirmCompositeWidgets();

        if (!array_key_exists($key, $this->composite_widgets)) {
            throw new SwatWidgetNotFoundException(
                sprintf(
                    "Composite widget with key of '%s' not found in %s. Make sure " .
                        "the composite widget was created and added to this widget.",
                    $key,
                    get_class($this)
                ),
                0,
                $key
            );
        }

        return $this->composite_widgets[$key];
    }