app: prevent fragments being wrapped in <undefined> element

js/erp5_loader.js

@@ -6134,6 +6134,9 @@
           case "item":
             generator = {"fragment": pass.content_dict.content};
             break;
+          case (undefined):
+            generator = {"fragment": document.createDocumentFragment()};
+            break;
           default:
             generator = {"fragment": factory.element(pass.content_dict)};
             break;