MSI-1542: Provide MSI support for Shipment Web API endpoint

Author: IvanPletnyov

app/code/Magento/Sales/Model/Order/ShipmentDocumentFactory.php

@@ -68,6 +68,8 @@ public function __construct(
     }
 
     /**
+     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+     *
      * @param OrderInterface $order
      * @param ShipmentItemCreationInterface[] $items
      * @param ShipmentTrackCreationInterface[] $tracks
@@ -97,7 +99,9 @@ public function create(
             $shipmentItems
         );
 
-        $this->extensionAttributesProcessor->execute($shipment, $arguments);
+        if (null !== $arguments) {
+            $this->extensionAttributesProcessor->execute($shipment, $arguments);
+        }
 
         foreach ($tracks as $track) {
             $hydrator = $this->hydratorPool->getHydrator(

app/code/Magento/Sales/Model/Order/ShipmentDocumentFactory/ExtensionAttributesProcessor.php

@@ -48,11 +48,8 @@ public function __construct(
      */
     public function execute(
         ShipmentInterface $shipment,
-        ShipmentCreationArgumentsInterface $arguments = null
+        ShipmentCreationArgumentsInterface $arguments
     ): void {
-        if (null === $arguments) {
-            return;
-        }
         $shipmentExtensionAttributes = [];
         if (null !== $shipment->getExtensionAttributes()) {
             $shipmentExtensionAttributes = $this->extensionAttributesProcessor->buildOutputDataArray(