protected function removeState($key)
    {
        if (!Yii::$app->has('session')) {
            return true;
        }
        /* @var \yii\web\Session $session */
        $session = Yii::$app->get('session');
        $key = $this->getStateKeyPrefix() . $key;
        $session->remove($key);
        return true;
    }