I am trying to check whether an user email is set or not. I am able to get the ones that are set to NULL but I am missing on the ones that have an empty string as the value. Here is my attempt:

```
$user = $this->createQueryBuilder('u')
        ->where('(u.email IS NULL OR u.email = :empty)')
        ->setParameter('empty', "''")
        ->getQuery()->getResult()
;

```

I have no problem getting the NULL emails but I fail to get the empty string emails. Is there any way to accomplish this or is it not supported in DQL?