public function preSetData(FormEvent $event)
    {  
        $entity = $event->getData();

        if ($entity instanceof ImageInterface && null !== $entity->getId()){
            try{
                $this->imageManager->copyImagesToTemporaryDirectory($entity);
            } catch(\Gaufrette\Exception\FileNotFound $e){ 
                $event->setData(null);
            }
        }
    }