public function getNotificationCount($notifiable_identifier, $notifiable_class, $seen = null)
    {
        $qb = $this->getNotificationCoundQb($notifiable_identifier, $notifiable_class);

        if ($seen !== null) {
            $whereSeen = $seen ? 1 : 0;
            $qb
                ->andWhere('nn.seen = :seen')
                ->setParameter('seen', $whereSeen);
        }
        return $qb->getQuery()->getSingleScalarResult();
    }