Bugsnag & Emberjs : application.lookup is not a function

I'm trying to configure Bugsnag in my EmberJs(v2.12) application.

I am following this example: http://ift.tt/2st6cX7

But I have an error in the browser telling that the lookup is not a function.

app/initializer/bugsnag.js

import Ember from 'ember';
import config from '../config/environment';

export default {
  name: 'bugsnag',

  initialize: function(appInstance) {

      // appInstance.lookup is not a function
      var appController = appInstance.lookup('controller:application');
  }
};

Someone would have a way to access the application controller in an emberjs initializer?

Or maybe a better solution to install bugsnag on an Emberjs application?