protected function handleThumb()
    {
        if ($this->thumbId !== $this->content->thumb_id) {
            if ($this->thumbId === null) {
                return $this->content->thumb()->dissociate();
            }

            $thumb = File::find($this->thumbId);
            if (empty($thumb)) {
                throw new InvalidArgumentException('Thumbnail file does not exist');
            }
            return $this->content->thumb()->associate($thumb);
        }
    }