code: protected function generateNumber(ShipmentInterface $shipment)
      {
          if (0 == strlen($shipment->getNumber())) {
              $this->numberGenerator->generate($shipment);
  
              return true;
          }
  
          return false;
      }
docs: Generates the number.
  
  @param ShipmentInterface $shipment
  
  @return bool Whether the shipment has been generated or not.