Only run sortable handler if specified

modules/backend/formwidgets/repeater/assets/js/repeater.js

@@ -239,12 +239,14 @@
     Repeater.prototype.onSortStop = function($item, container, callback, event) {
         var endIndex = $item.index()
 
+        if (this.options.sortableHandler) {
             this.$el.request(this.options.sortableHandler, {
                 data: {
                     _repeater_index: this.sortingStartIndex,
                     _repeater_new_index: endIndex
                 }
             })
+        }
 
         callback($item, container, callback, event)
     }