A missing context in the demo causes the error

[mikekosulin]

Tried to open the demo, but got this

═══════════════════════╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY╞═══════════════════════
The following _CastError was thrown building PathStack(dirty, dependencies:
[_InheritedPathStack],
state: PathStackState#e449a(ticker active)):
type 'Null' is not a subtype of type '_InheritedNavStackController' in type cast

The relevant error-causing widget was:
  PathStack
  ./flutter_nav_stack/example/lib/advanced_tabs_demo.dart:16:40

fixed this stuff and wrapped in a SafeArea widget for better experience