/**
  * Finds the Common model based on its slug value.
  * If the model is not found, a 404 HTTP exception will be thrown.
  *
  * @param string $slug
  * @return Common the loaded model
  * @throws NotFoundHttpException if the model cannot be found
  */
 protected function findCommon($slug)
 {
     if (($model = Common::findOne(['slug' => $slug, 'status' => Common::STATUS_VISIBLE])) !== null) {
         return $model;
     } else {
         throw new NotFoundHttpException('The requested page does not exist.');
     }
 }