Symfony2 Doctrine Expr 'IS NOT NULL'

You can use isNotNull:

'query_builder' => function ($er){
    $qb = $er->createQueryBuilder('p');
    $qb
        ->where($qb->expr()->andx(
            $qb->expr()->in('p', '?1'),
            $qb->expr()->isNotNull('p.location')
        ))
        ->setParameter(1, $this->totalScope);

    return $qb;
},

You can also use DQL in your queryBuilder, which is much less ugly IMO.

Quick and dirty example from a controller:

$repo = $this->getDoctrine()->getRepository('AcmeBundle:Transaction');
$query = $repo->createQueryBuilder('t')
    ->where('t.timestamp > :timestamp')
    ->andWhere('t.pinNumber IS NOT NULL')
    ->setParameter('timestamp', new \DateTime('1 day ago'))
    ->getQuery()
;

Easier to read in my estimation.