MAGETWO-83627: 11532: Duplicate Simple Product Throws Error: Undefined offset: 0 in SaveHandler.php on line 122 #12001

Author: Oleksii Korshenko

app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php

@@ -119,7 +119,9 @@ private function mergeCategoryLinks($newCategoryPositions, $oldCategoryPositions
 
             if ($key === false) {
                 $result[] = $newCategoryPosition;
-            } elseif ($oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']) {
+            } elseif (isset($oldCategoryPositions[$key])
+                && $oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']
+            ) {
                 $result[] = $newCategoryPositions[$key];
                 unset($oldCategoryPositions[$key]);
             }

app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php

@@ -197,6 +197,21 @@ public function getCategoryDataProvider()
                 ],
                 [], //affected category_ids
             ],
+            [
+                [3], //model category_ids
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ], // dto category links
+                [
+                    ['category_id' => 3, 'position' => 10],
+                ],
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ],
+                [3, 4], //affected category_ids
+            ],
         ];
     }