fix removing moderators

src/groups/editGroup.js

@@ -79,12 +79,10 @@ export default class NewGroup extends EditView {
   }
 
   beforeSubmit() {
-    const { data } = this.form;
-    // exchange moderator object with string of id
-    this.submit({
-      ...data,
-      moderator: data.moderator ? data.moderator._id : undefined,
-    }).then(() => this.controller.changeModus('view'));
+    const data = Object.assign({}, this.form.data);
+    // exchange moderator object with string of id, will return null if moderator is null
+    data.moderator = data.moderator ? data.moderator._id : null;
+    this.submit(data).then(() => this.controller.changeModus('view'));
   }
 
   view() {