SHouldn't be null returned getAggregateRoot

DossierAggregateRepository.php

final class DossierAggregateRepository extends AggregateRepository implements DossierRepository
{
    public function save(Dossier $dossier): void
    {
        $this->saveAggregateRoot($dossier);
    }

    public function get(DossierId $dossierId): ?Dossier
    {
        $ar = $this->getAggregateRoot((string) $dossierId);

        if (get_class($ar) !== Dossier::class) {
          return null;
        }

        return $ar;
    }
}