def load_apartment_by_doorbell_id(doorbell_id):
        # type: (int) -> Optional[ApartmentDTO]
        apartment_orm = Apartment.select().where(Apartment.doorbell_rebus_id == doorbell_id).first()
        if apartment_orm is None:
            return None
        apartment_dto = ApartmentMapper.orm_to_dto(apartment_orm)
        return apartment_dto