MAGETWO-62271: Inconsistent saving of Stock Data

Author: Valeriy Nayda

app/code/Magento/Catalog/Model/Product/Copier.php

@@ -60,12 +60,7 @@ public function copy(\Magento\Catalog\Model\Product $product)
         /** @var \Magento\Catalog\Model\Product $duplicate */
         $duplicate = $this->productFactory->create();
         $productData = $product->getData();
-        if (isset($productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY])) {
-            $extensionAttributes = $productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY];
-            if (null !== $extensionAttributes->getStockItem()) {
-                $extensionAttributes->setData('stock_item', null);
-            }
-        }
+        $productData = $this->removeStockItem($productData);
         $duplicate->setData($productData);
         $duplicate->setOptions([]);
         $duplicate->setIsDuplicate(true);
@@ -123,4 +118,21 @@ private function getMetadataPool()
         }
         return $this->metadataPool;
     }
+
+    /**
+     * Remove stock item
+     *
+     * @param array $productData
+     * @return array
+     */
+    private function removeStockItem(array $productData)
+    {
+        if (isset($productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY])) {
+            $extensionAttributes = $productData[ProductInterface::EXTENSION_ATTRIBUTES_KEY];
+            if (null !== $extensionAttributes->getStockItem()) {
+                $extensionAttributes->setData('stock_item', null);
+            }
+        }
+        return $productData;
+    }
 }