MAGETWO-28252: Catalog Inventory Integration API

 - fix static failure
 - fix REST and SOAP failures

Author: Mike Weis

app/code/Magento/CatalogInventory/Api/Data/StockItemInterface.php

@@ -55,7 +55,7 @@ interface StockItemInterface extends ExtensibleDataInterface
     const CUSTOMER_GROUP_ID = 'customer_group_id';
 
     /**
-     * @return int
+     * @return int|null
      */
     public function getItemId();
 
@@ -66,7 +66,7 @@ public function getItemId();
     public function setItemId($itemId);
 
     /**
-     * @return int
+     * @return int|null
      */
     public function getProductId();
 
@@ -79,7 +79,7 @@ public function setProductId($productId);
     /**
      * Retrieve Website Id
      *
-     * @return int
+     * @return int|null
      */
     public function getWebsiteId();
 
@@ -94,7 +94,7 @@ public function setWebsiteId($websiteId);
     /**
      * Retrieve stock identifier
      *
-     * @return int
+     * @return int|null
      */
     public function getStockId();
 

app/code/Magento/CatalogInventory/Model/Plugin/AfterProductLoad.php

@@ -37,7 +37,7 @@ public function __construct(
      * @param \Magento\Catalog\Model\Product $product
      * @return \Magento\Catalog\Model\Product
      */
-    public function afterLoad($product)
+    public function afterLoad(\Magento\Catalog\Model\Product $product)
     {
         $productExtension = $product->getExtensionAttributes();
         if ($productExtension === null) {

app/code/Magento/CatalogInventory/Model/StockRegistry.php

@@ -185,9 +185,7 @@ public function updateStockItemBySku($productSku, \Magento\CatalogInventory\Api\
         $origStockItem = $this->getStockItem($productId, $websiteId);
         $data = $stockItem->getData();
         if ($origStockItem->getItemId()) {
-            if (isset($data['item_id'])) {
-                unset($data['item_id']);
-            }
+            unset($data['item_id']);
         }
         $origStockItem->addData($data);
         $origStockItem->setProductId($productId);