public function __construct(UserRepository $users)
    {
        $this->users = $users;
    }


    public function execute(Passenger $user, int $cityId, string $companyName = '')
    {
        $city = $this->users->getCityReferenceById($cityId);
        $user->addCity($city);
        ....
    }

public function getCityReferenceById(int $cityId): City
{
    return $this->em->getReference(City::class, $cityId);
}