mongoose query with function 28req 2c res 2c next 29

1router.post('/travellers',
2    passport.authenticate('jwt', { "session": false }), function(req, res, next) {
3    var pickup_location = req.body.pickup_location;
4    var delivery_location = req.body.delivery_location;
5    var date = req.body.date;
6    var sender = req.user._id;
7    var locals = {
8        travellers: [],
9        senders: []
10    };
11
12    async.series([
13        // Load travels first
14        function(callback) {
15            Travel.find({ "date": date }, function (err, travels) {
16                if (err) return callback(err);
17                locals.travels = travels;
18                callback();
19            });
20        },
21        // Load users (won't be called before task 1's "task callback" has been called)
22        function(callback) {
23            async.forEach(locals.travels, function (travel, callback) {
24                User.findById(travel.traveller, function (err, user) {
25                    if (err) return callback(err);
26                    data = {
27                        "name": user.name,
28                        "email": user.email,
29                        "phone": user.phone,
30                        "image_url": user.image_url,
31                        "type": "traveller"
32                    };
33                    console.log(data);
34                    local.travellers.push(data);
35                    callback();
36                });
37            }, function (err) {
38                if (err) return callback(err);
39                            callback();
40            });
41        }
42    ], function(err) { /* This function gets called after 
43          the two tasks have called their "task callbacks" */
44        if (err) return next(err);
45        //Here locals will be populated with `travellers` and `senders`
46        //Just like in the previous example
47        console.log(locals);
48        console.log(locals.travellers);
49        res.json(locals.travellers);
50    });
51});