closes #4881

src/groups/membership.js

@@ -153,11 +153,7 @@ module.exports = function(Groups) {
 				path: '/groups/' + utils.slugify(groupName)
 			}),
 			function (notification, next) {
-				if (!notification) {
-					return next();
-				}
-
-				notifications.push(notification, [uid]);
+				notifications.push(notification, [uid], next);
 			}
 		], callback);
 	};

src/notifications.js

@@ -163,7 +163,7 @@ var utils = require('../public/src/utils');
 	Notifications.push = function(notification, uids, callback) {
 		callback = callback || function() {};
 
-		if (!notification.nid) {
+		if (!notification || !notification.nid) {
 			return callback();
 		}