/**
  * @see parent::check()
  */
 function check()
 {
     if ($msg = parent::check()) {
         return $msg;
     }
     if ($this->location_id) {
         $this->completeField("object_id", "object_class");
         $location = $this->loadRefLocation();
         if ($location->object_class !== $this->object_class || $location->object_id != $this->object_id) {
             return "Le stock doit être associé à un emplacement de '" . $this->loadTargetObject() . "'";
         }
     }
     return null;
 }