app.getActiveNav().setRoot() stopped working after upgrading to rc0

Ionic Framework ionic-v3
1

In app.ts, I used to use

goFooPage) {
  this.app.getActiveNav().setRoot(FooPage);
}

After upgrading to rc0, it stopped working, without any error

according to doc, I’ve tried the following in app.component.ts

this.app.getRootNav().setRoot(FooPage)
and 
this.nav.setRoot(FooPage)

doesn’t work either.