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    public function getOrdersCount(CarrierId $carrierId): int
    {
        $qb = $this->connection->createQueryBuilder();

        $count = $qb->select('COUNT(*)')
            ->from($this->prefix . 'order_carrier', 'oc')
            ->where('oc.id_carrier = :carrierId')
            ->setParameter('carrierId', $carrierId->getValue())
            ->executeQuery()
            ->fetchOne();

        return (int)$count;
    }

Add (int)  to the $count

edit src\Adapter\Carrier\Repository\CarrierRepository.php