/**
  * Finds the Rental model based on its primary key value.
  * If the model is not found, a 404 HTTP exception will be thrown.
  * @param integer $rental_id
  * @return Rental the loaded model
  * @throws HttpException if the model cannot be found
  */
 protected function findModel($rental_id)
 {
     if (($model = Rental::findOne($rental_id)) !== null) {
         return $model;
     } else {
         throw new HttpException(404, 'The requested page does not exist.');
     }
 }