code: private function initializeRelayPoint(ShipmentInterface $shipment)
      {
          // Abort if shipment method is not defined
          if (null === $method = $shipment->getMethod()) {
              // Clear the relay point if it is set
              if (null !== $shipment->getRelayPoint()) {
                  $shipment->setRelayPoint(null);
              }
  
              return;
          }
  
          $gateway = $this->registry->getGateway($method->getGatewayName());
  
          // If gateway does not support relay point
          if (!$gateway->supports(GatewayInterface::CAPABILITY_RELAY)) {
              // Clear the relay point if it is set
              if (null !== $shipment->getRelayPoint()) {
                  $shipment->setRelayPoint(null);
              }
  
              return;
          }
  
          // Set default relay point
          if (null !== $relayPoint = $shipment->getSale()->getRelayPoint()) {
              $shipment->setRelayPoint($relayPoint);
          }
      }
docs: Initializes the shipment's relay point.
  
  @param ShipmentInterface $shipment