Shipment/Builder/ShipmentBuilder.php
private function initializeMethod(ShipmentInterface $shipment)
    {
        // Abort if shipment's method is defined
        if (null !== $shipment->getMethod()) {
            return;
        }

        $sale = $shipment->getSale();

        // Abort if default method is not defined
        if (null === $method = $sale->getShipmentMethod()) {
            return;
        }

        $gateway = $this->registry->getGateway($method->getGatewayName());

        // Set shipment method if supported
        if (!$shipment->isReturn() && $gateway->supports(GatewayInterface::CAPABILITY_SHIPMENT)) {
            $shipment->setMethod($method);

            return;
        }

        // Set return method if supported
        if ($shipment->isReturn() && $gateway->supports(GatewayInterface::CAPABILITY_RETURN)) {
            $shipment->setMethod($method);

            return;
        }
    }
private function initializeMethod(ShipmentInterface $shipment)
    {
        // Abort if shipment's method is defined
        if (null !== $shipment->getMethod()) {
            return;
        }

        $sale = $shipment->getSale();

        // Abort if default method is not defined
        if (null === $method = $sale->getShipmentMethod()) {
            return;
        }

        $gateway = $this->registry->getGateway($method->getGatewayName());

        // Set shipment method if supported
        if (!$shipment->isReturn() && $gateway->supports(GatewayInterface::CAPABILITY_SHIPMENT)) {
            $shipment->setMethod($method);

            return;
        }

        // Set return method if supported
        if ($shipment->isReturn() && $gateway->supports(GatewayInterface::CAPABILITY_RETURN)) {
            $shipment->setMethod($method);

            return;
        }
    }
Initializes the shipment's method.

@param ShipmentInterface $shipment