public function isQueued(string $alias): bool
    {
        $query = $this->createQueryBuilder('c')
            ->where('c.alias = :alias')
            ->andWhere('c.ended is NULL')
            ->setParameter('alias', $alias)
            ->getQuery();

        try {
            $result = $query->setMaxResults(1)->getOneOrNullResult();
            if ($result) {
                return true;
            }
        } catch (NonUniqueResultException $e) {
            return false;
        }

        return false;
    }