issue-39329-Invalid SKU Handling for Linked Products in Magento

app/code/Magento/Catalog/Controller/Adminhtml/Product/Save.php

@@ -139,6 +139,9 @@ public function execute()
                 }
 
                 $originalSku = $product->getSku();
+                if($originalSku == 0){
+                    throw new \Magento\Framework\Exception\LocalizedException(__("SKU cannot be zero."));                                 
+                }
                 $canSaveCustomOptions = $product->getCanSaveCustomOptions();
                 $product->save();
                 $this->handleImageRemoveError($data, $product->getId());

app/code/Magento/Catalog/Model/ProductLink/Repository.php

@@ -139,7 +139,7 @@ public function save(\Magento\Catalog\Api\Data\ProductLinkInterface $entity)
                 . 'Please ensure the parent product SKU is provided and try again.'
             ));
         }
-        if (!$entity->getLinkedProductSku()) {
+        if ($entity->getLinkedProductSku() === null || $entity->getLinkedProductSku() === '') {
             throw new CouldNotSaveException(__('The linked product SKU is invalid. Verify the data and try again.'));
         }
         $linkedProduct = $this->productRepository->get($entity->getLinkedProductSku());

app/code/Magento/Catalog/i18n/en_US.csv

@@ -868,3 +868,4 @@ Details,Details
 "Add To Compare","Add To Compare"
 "Learn more","Learn more"
 "Recently Viewed","Recently Viewed"
+"SKU cannot be zero.","SKU cannot be zero."