Update custom-wizard-admin.js.es6

assets/javascripts/discourse/models/custom-wizard-admin.js.es6

@@ -12,7 +12,7 @@ const GUEST_GROUP_ID = -1;
 const CustomWizardAdmin = EmberObject.extend({
   @discourseComputed("permitted.@each.output")
   allowGuests(permitted) {
-    return permitted.filter((p) => p.output.includes(GUEST_GROUP_ID)).length;
+    return permitted && permitted.filter((p) => p.output.includes(GUEST_GROUP_ID)).length;
   },
 
   save(opts) {