TypeError: b is undefined

I have an Ionic2 app, that has just stopped working (not sure why).

The following command:

ionic serve

Builds the app with no errors, but when http://localhost:8100/ is loaded into the browser, I get:

TypeError: b is undefined

In order to debug this I tried to put a console.log at the top of app.ts constructor, but this is not being printed.

Does anyone have any ideas what is wrong, or were I should look to try diagnose this?

Thanks

UPDATE

I have been doing some more debugging, and I have found that this is related to inheritance of a variable I think.

I have the following code:

search.ts

export class SearchPage extends SearchSubParentPage {

  constructor(ref: ChangeDetectorRef, nav: NavController, private viewCtrl: ViewController, jobService: JobService, personService: PersonService, utilityService: UtilityService, navParams: NavParams, popoverController: PopoverController, events: Events, platform: Platform, alertCtrl: AlertController, loadingController: LoadingController) {
    super(ref, nav, viewCtrl, jobService, personService, utilityService, navParams, popoverController, events, platform, alertCtrl, loadingController, false, 0);
  }

searchSubParent.ts

export class SearchSubParentPage extends SearchParent {

private popoverController: PopoverController = null;

  constructor(ref: ChangeDetectorRef, nav: NavController, viewCtrl: ViewController, jobService: JobService, personService: PersonService, utilityService: UtilityService, navParams: NavParams, popoverController: PopoverController, events: Events, platform: Platform, alertCtrl: AlertController, loadingController: LoadingController, favourite: boolean, jobType: number) {
    this.popoverController = popoverController;
}

As you can see, the popoverController object is passed via the constructor to the parent SearchSubParentPage.

If I have the following line of code in SearchSubParentPage, I get the error:

this.popover = this.popoverController.create(SearchJobsPopOverPage, {...

If I comment it out, it works. So this suggests that there is something wrong with the way I pass popoverController to the parent (I have the same issue with the nav object too).

If I console.log either this.popoverController or this.nav, they appear to be fine (i.e. not undefined or null).

on which version of ionic are you and what app scripts are you using?

please post the output of
ionic info

Thanks for the reply. Here you go:

Your system information:

Cordova CLI: 6.4.0
Ionic Framework Version: 2.0.0-beta.11
Ionic CLI Version: 2.1.0
Ionic App Lib Version: 2.0.0-beta.20
OS:
Node Version: v6.2.2

If I make the object public, it works, not sure why.

change:

private popoverController: PopoverController = null;

to:

public popoverController: PopoverController = null;