protected function ensureValidResult() {
        $deliveryExecution = ServiceProxy::singleton()->getDeliveryExecution($this->instanceCache[$this->currentInstance]);
       try {
           $deliveryExecution->getDelivery();
       } catch (\common_exception_NotFound $e) {
           $message = 'Skip result '. $deliveryExecution->getIdentifier(). ' with message '.$e->getMessage();
           \common_Logger::e($message);
           $this->next();
       }
    }