#13177: Can't save attributes on a configurable product.

- fix error while saving configurable product after validation error.

Author: al.kravchuk

app/code/Magento/ConfigurableProduct/view/adminhtml/web/js/variations/variations.js

@@ -407,15 +407,17 @@ define([
          *   - associated_product_ids_serialized.
          */
         serializeData: function () {
-            this.source.data['configurable-matrix-serialized'] =
-                JSON.stringify(this.source.data['configurable-matrix']);
-
-            delete this.source.data['configurable-matrix'];
-
-            this.source.data['associated_product_ids_serialized'] =
-                JSON.stringify(this.source.data['associated_product_ids']);
+            if (this.source.data['configurable-matrix']) {
+                this.source.data['configurable-matrix-serialized'] =
+                    JSON.stringify(this.source.data['configurable-matrix']);
+                delete this.source.data['configurable-matrix'];
+            }
 
-            delete this.source.data['associated_product_ids'];
+            if (this.source.data['associated_product_ids']) {
+                this.source.data['associated_product_ids_serialized'] =
+                    JSON.stringify(this.source.data['associated_product_ids']);
+                delete this.source.data['associated_product_ids'];
+            }
         },
 
         /**