_routerExtensions.back() causes crash after closing modal

[jeffswitzer]

Environment
have only tried on android

Describe the bug
After closing a modal, back navigation via routerExtension doesn't work resulting in a runtime error.

To Reproduce
Open this nativescript playground

1. using router, navigate from component1 to component2
2. open a modal inside component2
3. close the modal
4. click back to attempt to navigate back from component2 to component1
5. runtime error says: ERROR TypeError: Cannot read property 'isPageNavigationBack' of undefined

Expected behavior
The back navigation should take you back to component 1

Additional context
This may be related to #1350

[tsonevn]

Hi @jeffswitzer,
I was able to recreate the issue while using your demo app and will mark this problem as a bug. It seems that there is an issue with the router-outlet. As a workaround, I would suggest using page-router-outlet. Check out the example here.