magento/magento2#12705: Integrity constraint violation error after reordering...

magento/magento2#12705: Integrity constraint violation error after reordering product with custom options

- Fixed issue by updating options if parent item is same for more than one product
- Fixed issue for reorder in admin while checking the availability of product, which is not available in case of associate product.
- Fixed Null coalescing operator issue

app/code/Magento/ConfigurableProductSales/Model/Order/Reorder/OrderedProductAvailabilityChecker.php

@@ -45,7 +45,7 @@ class OrderedProductAvailabilityChecker implements OrderedProductAvailabilityChe
     public function isAvailable(Item $item)
     {
         $buyRequest = $item->getBuyRequest();
-        $superAttribute = isset($buyRequest->getData()['super_attribute']) ? $buyRequest->getData()['super_attribute'] : [];
+        $superAttribute = $buyRequest->getData()['super_attribute'] ?? [];
         $connection = $this->getConnection();
         $select = $connection->select();
         $orderItemParentId = $item->getParentItem()->getProductId();