Keystone js - populateRelated fields appearing as undefined

Question

Every Application has a 1 to 1 relationship with a user. Every Trip has n Applications.

Here's my following code for populating all User (students) data in the Applications of all trips:

view.on('init', function(next) {
    Trip.model.find()
    .exec(function(err, trips){
        keystone.populateRelated(trips, 'students[user]', function(err) {
            locals.trips = trips;
            next();
        });
    });

});

Here is the relationship that Trips has with Applications (StudentApp):

Trip.relationship({ ref: 'StudentApp', refPath: 'finalTrip', path: 'students' });

Now on the front end, I can print the stringified JSON of a user just fine:

each trip in trips
  each app in trip.students
      p=app.user

However the moment I try to access a field e.g app.user._id I get the following error:

Cannot read property '_id' of undefined

I get the feeling it's an asynchronous issue, but I can't for the life of me figure out how to fix this.

Help would be much appreciated. Thanks.