final protected function getCompositeRenderer($key)
    {
        $this->confirmCompositeRenderers();

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

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