ConvertBlankToNullSubscriber.php

<?php

namespace Model\Events;

use Doctrine\ORM\Event\PreFlushEventArgs;
use Kdyby\Events\Subscriber;
use Nette;

class ConvertBlankToNullSubscriber extends Nette\Object implements Subscriber
{

	public function getSubscribedEvents()
	{
		return array('preFlush');
	}



	public function preFlush(PreFlushEventArgs $args)
	{
		$em = $args->getEntityManager();
		$uow = $em->getUnitOfWork();
		foreach (array_merge($uow->getScheduledEntityInsertions(), $uow->getScheduledEntityUpdates()) as $entity) {
			$metadata = $em->getMetadataFactory()->getMetadataFor($entity::class);
			foreach($metadata->getFieldNames() as $field) {
				if($metadata->getTypeOfField($field) === "string" and $entity->$field === "") {
					$entity->$field = null;
				}
			}
		}
	}

}