public function markAsUnread($uid)
    {
        if(!$object = $this->model->find($uid)) {
            abort(404);
        }

        $this->authorize('update', $object);

        if (!is_null($object->read_at)) {
            $object->forceFill(['read_at' => null])->save();
        }

        \Cache::tags('response')->flush();

        return $this->successJsonResponse();
    }