public function postSetData(FormEvent $event)
    {
        $collection = $event->getData();
        $form = $event->getForm();

        if ($collection instanceof PersistentCollection){
            foreach ($collection as $key => $file){
                if ($file instanceof MultiFileInterface){
                    try {
                        $this->fileManager->copyFileToTemporaryDirectory($file);
                    } catch (\Gaufrette\Exception\FileNotFound $e) {
                        $form->remove($key);
                        $collection->removeElement($file);
                    }
                }
            }
        }
    }