Dart APIunself_appAppShellnavigator navigator property Null safety GlobalKey<NavigatorState> navigator final Implementation static final navigator = GlobalKey<NavigatorState>(debugLabel: 'AppShell'); unself_app unself_app AppShell navigator property AppShell class Properties child hashCode key runtimeType Methods createElement createState debugDescribeChildren debugFillProperties noSuchMethod toDiagnosticsNode toString toStringDeep toStringShallow toStringShort Operators operator == Static properties defaultRoute navigator