public function toArray()
    {
        $array = [];

        if (! empty($this->data)) {
            $array['data'] = $this->data->toIdentifier();
        }

        if (! empty($this->meta)) {
            $array['meta'] = $this->meta;
        }

        if (! empty($this->links)) {
            $array['links'] = $this->links;
        }

        return $array;
    }