Remove the `nullOk` parameter from `Navigator.of` and add `Navigator.maybeOf` (#70726)

Adds Navigator.maybeOf to replace calling Navigator.of(context, nullOk: true), and removes the nullOk parameter. Also changes Navigator.of to return a non-nullable value, and removes many (120!) instances of the ! operator, reducing the possible places where a null dereference could occur.

dev/integration_tests/flutter_gallery/lib/demo/cupertino/cupertino_navigation_demo.dart

@@ -117,7 +117,7 @@ class ExitButton extends StatelessWidget {
       ),
       onPressed: () {
         // The demo is on the root navigator.
-        Navigator.of(context, rootNavigator: true)!.pop();
+        Navigator.of(context, rootNavigator: true).pop();
       },
     );
   }
@@ -202,7 +202,7 @@ class Tab1RowItem extends StatelessWidget {
     final Widget row = GestureDetector(
       behavior: HitTestBehavior.opaque,
       onTap: () {
-        Navigator.of(context)!.push(CupertinoPageRoute<void>(
+        Navigator.of(context).push(CupertinoPageRoute<void>(
           title: colorName,
           builder: (BuildContext context) => Tab1ItemPage(
             color: color,
@@ -752,7 +752,7 @@ class CupertinoDemoTab3 extends StatelessWidget {
           const Padding(padding: EdgeInsets.only(top: 32.0)),
           GestureDetector(
             onTap: () {
-              Navigator.of(context, rootNavigator: true)!.push(
+              Navigator.of(context, rootNavigator: true).push(
                 CupertinoPageRoute<bool>(
                   fullscreenDialog: true,
                   builder: (BuildContext context) => Tab3Dialog(),
@@ -800,7 +800,7 @@ class Tab3Dialog extends StatelessWidget {
           child: const Text('Cancel'),
           padding: EdgeInsets.zero,
           onPressed: () {
-            Navigator.of(context)!.pop(false);
+            Navigator.of(context).pop(false);
           },
         ),
       ),

dev/integration_tests/flutter_gallery/lib/demo/material/full_screen_dialog_demo.dart

@@ -126,13 +126,13 @@ class FullScreenDialogDemoState extends State<FullScreenDialogDemo> {
             TextButton(
               child: const Text('CANCEL'),
               onPressed: () {
-                Navigator.of(context)!.pop(false); // Pops the confirmation dialog but not the page.
+                Navigator.of(context).pop(false); // Pops the confirmation dialog but not the page.
               },
             ),
             TextButton(
               child: const Text('DISCARD'),
               onPressed: () {
-                Navigator.of(context)!.pop(true); // Returning true to _onWillPop will pop again.
+                Navigator.of(context).pop(true); // Returning true to _onWillPop will pop again.
               },
             ),
           ],

dev/integration_tests/flutter_gallery/lib/demo/material/search_demo.dart

@@ -98,7 +98,7 @@ class _SearchDemoState extends State<SearchDemo> {
       floatingActionButton: FloatingActionButton.extended(
         tooltip: 'Back', // Tests depend on this label to exit the demo.
         onPressed: () {
-          Navigator.of(context)!.pop();
+          Navigator.of(context).pop();
         },
         label: const Text('Close demo'),
         icon: const Icon(Icons.close),

dev/integration_tests/flutter_gallery/lib/demo/material/text_form_field_demo.dart

@@ -151,11 +151,11 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
           actions: <Widget> [
             TextButton(
               child: const Text('YES'),
-              onPressed: () { Navigator.of(context)!.pop(true); },
+              onPressed: () { Navigator.of(context).pop(true); },
             ),
             TextButton(
               child: const Text('NO'),
-              onPressed: () { Navigator.of(context)!.pop(false); },
+              onPressed: () { Navigator.of(context).pop(false); },
             ),
           ],
         );

dev/integration_tests/flutter_gallery/lib/demo/shrine/login.dart

@@ -35,7 +35,7 @@ class _LoginPageState extends State<LoginPage> {
             // The login screen is immediately displayed on top of the Shrine
             // home screen using onGenerateRoute and so rootNavigator must be
             // set to true in order to get out of Shrine completely.
-            Navigator.of(context, rootNavigator: true)!.pop();
+            Navigator.of(context, rootNavigator: true).pop();
           },
         ),
       ),
@@ -95,7 +95,7 @@ class _LoginPageState extends State<LoginPage> {
                         // the Shrine home screen using onGenerateRoute and so
                         // rootNavigator must be set to true in order to get out
                         // of Shrine completely.
-                        Navigator.of(context, rootNavigator: true)!.pop();
+                        Navigator.of(context, rootNavigator: true).pop();
                       },
                       child: const Text('CANCEL'),
                     ),

dev/integration_tests/flutter_gallery/lib/demo/transformations/transformations_demo.dart

@@ -107,7 +107,7 @@ class _TransformationsDemoState extends State<TransformationsDemo> {
         TextButton(
           child: const Text('OK'),
           onPressed: () {
-            Navigator.of(context)!.pop();
+            Navigator.of(context).pop();
           },
         ),
       ],

dev/integration_tests/flutter_gallery/lib/demo/video_demo.dart

@@ -70,7 +70,7 @@ class VideoCard extends StatelessWidget {
       });
 
       controller!.setVolume(1.0);
-      Navigator.of(context)!.push(route);
+      Navigator.of(context).push(route);
     }
 
     return SafeArea(

packages/flutter/lib/src/cupertino/context_menu.dart

@@ -292,7 +292,7 @@ class _CupertinoContextMenuState extends State<CupertinoContextMenu> with Ticker
         return widget.previewBuilder!(context, animation, widget.child);
       },
     );
-    Navigator.of(context, rootNavigator: true)!.push<void>(_route!);
+    Navigator.of(context, rootNavigator: true).push<void>(_route!);
     _route!.animation!.addStatusListener(_routeAnimationStatusListener);
   }
 
@@ -686,7 +686,7 @@ class _ContextMenuRoute<T> extends PopupRoute<T> {
       parent: animation!,
       curve: const Interval(0.9, 1.0),
     ));
-    Navigator.of(context)!.pop();
+    Navigator.of(context).pop();
   }
 
   // Take measurements on the child and _ContextMenuSheet and update the

packages/flutter/lib/src/cupertino/route.dart

@@ -1060,7 +1060,7 @@ Future<T?> showCupertinoModalPopup<T>({
   RouteSettings? routeSettings,
 }) {
   assert(useRootNavigator != null);
-  return Navigator.of(context, rootNavigator: useRootNavigator)!.push(
+  return Navigator.of(context, rootNavigator: useRootNavigator).push(
     _CupertinoModalPopupRoute<T>(
       barrierColor: CupertinoDynamicColor.resolve(barrierColor, context),
       barrierDismissible: barrierDismissible,

packages/flutter/lib/src/material/about.dart

@@ -292,7 +292,7 @@ void showLicensePage({
 }) {
   assert(context != null);
   assert(useRootNavigator != null);
-  Navigator.of(context, rootNavigator: useRootNavigator)!.push(MaterialPageRoute<void>(
+  Navigator.of(context, rootNavigator: useRootNavigator).push(MaterialPageRoute<void>(
     builder: (BuildContext context) => LicensePage(
       applicationName: applicationName,
       applicationVersion: applicationVersion,
@@ -1342,8 +1342,8 @@ class _MasterDetailFlowState extends State<_MasterDetailFlow> implements _PageOp
             ? widget.masterPageBuilder!(c, false)
             : _MasterPage(
                 leading: widget.leading ??
-                    (widget.automaticallyImplyLeading && Navigator.of(context)!.canPop()
-                        ? BackButton(onPressed: () => Navigator.of(context)!.pop())
+                    (widget.automaticallyImplyLeading && Navigator.of(context).canPop()
+                        ? BackButton(onPressed: () => Navigator.of(context).pop())
                         : null),
                 title: widget.title,
                 centerTitle: widget.centerTitle,
@@ -1364,7 +1364,7 @@ class _MasterDetailFlowState extends State<_MasterDetailFlow> implements _PageOp
         onWillPop: () async {
           // No need for setState() as rebuild happens on navigation pop.
           focus = _Focus.master;
-          Navigator.of(context)!.pop();
+          Navigator.of(context).pop();
           return false;
         },
         child: BlockSemantics(child: widget.detailPageBuilder(context, arguments, null)),

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -669,7 +669,7 @@ Future<T?> showModalBottomSheet<T>({
   assert(debugCheckHasMediaQuery(context));
   assert(debugCheckHasMaterialLocalizations(context));
 
-  final NavigatorState navigator = Navigator.of(context, rootNavigator: useRootNavigator)!;
+  final NavigatorState navigator = Navigator.of(context, rootNavigator: useRootNavigator);
   return navigator.push(_ModalBottomSheetRoute<T>(
     builder: builder,
     capturedThemes: InheritedTheme.capture(from: context, to: navigator.context),

packages/flutter/lib/src/material/dialog.dart

@@ -978,7 +978,7 @@ Future<T?> showDialog<T>({
   assert(useRootNavigator != null);
   assert(debugCheckHasMaterialLocalizations(context));
 
-  final CapturedThemes themes = InheritedTheme.capture(from: context, to: Navigator.of(context, rootNavigator: useRootNavigator)!.context);
+  final CapturedThemes themes = InheritedTheme.capture(from: context, to: Navigator.of(context, rootNavigator: useRootNavigator).context);
   return showGeneralDialog(
     context: context,
     pageBuilder: (BuildContext buildContext, Animation<double> animation, Animation<double> secondaryAnimation) {

packages/flutter/lib/src/material/dropdown.dart

@@ -1206,7 +1206,7 @@ class _DropdownButtonState<T> extends State<DropdownButton<T>> with WidgetsBindi
       )
     ];
 
-    final NavigatorState navigator = Navigator.of(context)!;
+    final NavigatorState navigator = Navigator.of(context);
     assert(_dropdownRoute == null);
     _dropdownRoute = _DropdownRoute<T>(
       items: menuItems,

packages/flutter/lib/src/material/popup_menu.dart

@@ -842,7 +842,7 @@ Future<T?> showMenu<T>({
       semanticLabel ??= MaterialLocalizations.of(context).popupMenuLabel;
   }
 
-  final NavigatorState navigator = Navigator.of(context, rootNavigator: useRootNavigator)!;
+  final NavigatorState navigator = Navigator.of(context, rootNavigator: useRootNavigator);
   return navigator.push(_PopupMenuRoute<T>(
     position: position,
     items: items,
@@ -1060,7 +1060,7 @@ class PopupMenuButtonState<T> extends State<PopupMenuButton<T>> {
   void showButtonMenu() {
     final PopupMenuThemeData popupMenuTheme = PopupMenuTheme.of(context);
     final RenderBox button = context.findRenderObject()! as RenderBox;
-    final RenderBox overlay = Navigator.of(context)!.overlay!.context.findRenderObject()! as RenderBox;
+    final RenderBox overlay = Navigator.of(context).overlay!.context.findRenderObject()! as RenderBox;
     final RelativeRect position = RelativeRect.fromRect(
       Rect.fromPoints(
         button.localToGlobal(widget.offset, ancestor: overlay),

packages/flutter/lib/src/material/search.dart

@@ -60,7 +60,7 @@ Future<T?> showSearch<T>({
   assert(context != null);
   delegate.query = query ?? delegate.query;
   delegate._currentBody = _SearchBody.suggestions;
-  return Navigator.of(context)!.push(_SearchPageRoute<T>(
+  return Navigator.of(context).push(_SearchPageRoute<T>(
     delegate: delegate,
   ));
 }
@@ -294,7 +294,7 @@ abstract class SearchDelegate<T> {
   void close(BuildContext context, T result) {
     _currentBody = null;
     _focusNode?.unfocus();
-    Navigator.of(context)!
+    Navigator.of(context)
       ..popUntil((Route<dynamic> route) => route == _route)
       ..pop(result);
   }

packages/flutter/lib/src/widgets/routes.dart

@@ -664,7 +664,7 @@ class _DismissModalAction extends DismissAction {
 
   @override
   Object invoke(DismissIntent intent) {
-    return Navigator.of(context)!.maybePop();
+    return Navigator.of(context).maybePop();
   }
 }
 
@@ -1849,7 +1849,7 @@ Future<T?> showGeneralDialog<T extends Object?>({
   assert(pageBuilder != null);
   assert(useRootNavigator != null);
   assert(!barrierDismissible || barrierLabel != null);
-  return Navigator.of(context, rootNavigator: useRootNavigator)!.push<T>(_DialogRoute<T>(
+  return Navigator.of(context, rootNavigator: useRootNavigator).push<T>(_DialogRoute<T>(
     pageBuilder: pageBuilder,
     barrierDismissible: barrierDismissible,
     barrierLabel: barrierLabel,

packages/flutter/test/cupertino/route_test.dart

@@ -1652,7 +1652,7 @@ void main() {
           return RaisedButton(
             child: const Text('Home'),
             onPressed: () {
-              navigator = Navigator.of(context)!;
+              navigator = Navigator.of(context);
               assert(navigator != null);
               navigator.push<void>(r);
             },

packages/flutter/test/cupertino/scaffold_test.dart

@@ -322,7 +322,7 @@ void main() {
                     child: CupertinoButton(
                       child: const Text('Next'),
                       onPressed: () {
-                        Navigator.of(context)!.push(
+                        Navigator.of(context).push(
                           CupertinoPageRoute<void>(
                             builder: (BuildContext context) {
                               return CupertinoPageScaffold(
@@ -333,7 +333,7 @@ void main() {
                                   child: CupertinoButton(
                                     child: const Text('Back'),
                                     onPressed: () {
-                                      Navigator.of(context)!.pop();
+                                      Navigator.of(context).pop();
                                     },
                                   ),
                                 ),

packages/flutter/test/cupertino/tab_test.dart

@@ -40,7 +40,7 @@ void main() {
             return CupertinoButton(
               child: const Text('go to second page'),
               onPressed: () {
-                Navigator.of(context)!.pushNamed('/2');
+                Navigator.of(context).pushNamed('/2');
               },
             );
           },
@@ -131,7 +131,7 @@ void main() {
             return CupertinoButton(
               child: const Text('go to second page'),
               onPressed: () {
-                Navigator.of(context)!.pushNamed('/2');
+                Navigator.of(context).pushNamed('/2');
               },
             );
           },
@@ -156,7 +156,7 @@ void main() {
             return CupertinoButton(
               child: const Text('go to second page'),
               onPressed: () {
-                Navigator.of(context)!.pushNamed('/2');
+                Navigator.of(context).pushNamed('/2');
               },
             );
           },
@@ -245,7 +245,7 @@ void main() {
           builder: (BuildContext context) => CupertinoButton(
             child: const Text('home'),
             onPressed: () {
-              Navigator.of(context)!.restorablePushNamed('/2');
+              Navigator.of(context).restorablePushNamed('/2');
             },
           ),
           routes: <String, WidgetBuilder>{
@@ -269,7 +269,7 @@ void main() {
     expect(find.text('home'), findsNothing);
     expect(find.text('second route'), findsOneWidget);
 
-    Navigator.of(tester.element(find.text('second route')))!.pop();
+    Navigator.of(tester.element(find.text('second route'))).pop();
     await tester.pumpAndSettle();
 
     expect(find.text('home'), findsOneWidget);
@@ -280,7 +280,7 @@ void main() {
     expect(find.text('home'), findsNothing);
     expect(find.text('second route'), findsOneWidget);
 
-    Navigator.of(tester.element(find.text('second route')))!.pop();
+    Navigator.of(tester.element(find.text('second route'))).pop();
     await tester.pumpAndSettle();
 
     expect(find.text('home'), findsOneWidget);

packages/flutter/test/material/app_test.dart

@@ -100,7 +100,7 @@ void main() {
             return Material(
               child: ElevatedButton(
                 child: const Text('X'),
-                onPressed: () { Navigator.of(context)!.pushNamed('/next'); },
+                onPressed: () { Navigator.of(context).pushNamed('/next'); },
               ),
             );
           }
@@ -258,7 +258,7 @@ void main() {
                   child: ElevatedButton(
                       child: const Text('X'),
                       onPressed: () async {
-                        result = Navigator.of(context)!.pushNamed<Object?>('/a');
+                        result = Navigator.of(context).pushNamed<Object?>('/a');
                       },
                   ),
                 );
@@ -270,7 +270,7 @@ void main() {
                 child: ElevatedButton(
                   child: const Text('Y'),
                   onPressed: () {
-                    Navigator.of(context)!.pop('all done');
+                    Navigator.of(context).pop('all done');
                   },
                 ),
               );

packages/flutter/test/material/dialog_test.dart

@@ -1813,7 +1813,7 @@ void main() {
             SimpleDialogOption(
               child: const Text('X'),
               onPressed: () {
-                Navigator.of(context)!.pop();
+                Navigator.of(context).pop();
               },
             ),
           ],

packages/flutter/test/material/inherited_theme_test.dart

@@ -41,7 +41,7 @@ void main() {
                           ElevatedButton(
                             child: const Text('push unwrapped'),
                             onPressed: () {
-                              Navigator.of(context)!.push<void>(
+                              Navigator.of(context).push<void>(
                                 MaterialPageRoute<void>(
                                   // The primaryBox will see the default Theme when built.
                                   builder: (BuildContext _) => primaryBox,
@@ -52,7 +52,7 @@ void main() {
                           ElevatedButton(
                             child: const Text('push wrapped'),
                             onPressed: () {
-                              Navigator.of(context)!.push<void>(
+                              Navigator.of(context).push<void>(
                                 MaterialPageRoute<void>(
                                   // Capture the shadow Theme.
                                   builder: (BuildContext _) => InheritedTheme.captureAll(context, primaryBox),
@@ -84,7 +84,7 @@ void main() {
     await tester.pumpAndSettle(); // route animation
     expect(containerColor(), primaryColor);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     // Show the route which contains primaryBox
@@ -181,7 +181,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The Banner will see the default BannerTheme when built.
                               builder: (BuildContext _) => banner,
@@ -192,7 +192,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow BannerTheme.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, banner),
@@ -234,7 +234,7 @@ void main() {
     expect(getTextStyle('hello').fontSize, bannerFontSize);
     expect(getTextStyle('hello').color, bannerTextColor);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));
@@ -271,7 +271,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The Banner will see the default BannerTheme when built.
                               builder: (BuildContext _) => divider,
@@ -282,7 +282,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow BannerTheme.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, divider),
@@ -316,7 +316,7 @@ void main() {
     expect(dividerBorder().color, dividerColor);
     expect(dividerBorder().width, dividerThickness);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));
@@ -375,7 +375,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The Banner will see the default BannerTheme when built.
                               builder: (BuildContext _) => listTiles,
@@ -386,7 +386,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow BannerTheme.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, listTiles),
@@ -429,7 +429,7 @@ void main() {
     expect(getIconStyle(selectedIconKey).color, tileSelectedColor);
     expect(getIconStyle(unselectedIconKey).color, tileIconColor);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));
@@ -475,7 +475,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The slider will see the default SliderTheme when built.
                               builder: (BuildContext _) => slider,
@@ -486,7 +486,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow SliderTheme.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, slider),
@@ -513,7 +513,7 @@ void main() {
     expect(sliderBox, paints..rrect(color: activeTrackColor)..rrect(color: inactiveTrackColor));
     expect(sliderBox, paints..circle(color: thumbColor));
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));
@@ -560,7 +560,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The slider will see the default ToggleButtonsTheme when built.
                               builder: (BuildContext _) => toggleButtons,
@@ -571,7 +571,7 @@ void main() {
                       ElevatedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow toggleButtons.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, toggleButtons),
@@ -603,7 +603,7 @@ void main() {
     expect(getTextColor('selected'), selectedButtonColor);
     expect(getTextColor('unselected'), buttonColor);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));
@@ -649,7 +649,7 @@ void main() {
                       RaisedButton(
                         child: const Text('push unwrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // The slider will see the default ButtonTheme when built.
                               builder: (BuildContext _) => buttons,
@@ -660,7 +660,7 @@ void main() {
                       RaisedButton(
                         child: const Text('push wrapped'),
                         onPressed: () {
-                          Navigator.of(context)!.push<void>(
+                          Navigator.of(context).push<void>(
                             MaterialPageRoute<void>(
                               // Capture the shadow toggleButtons.
                               builder: (BuildContext _) => InheritedTheme.captureAll(context, buttons),
@@ -695,7 +695,7 @@ void main() {
     expect(getButtonColor('disabled'), disabledButtonColor);
     expect(getButtonColor('enabled'), buttonColor);
 
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route animation
 
     await tester.tap(find.text('push unwrapped'));

packages/flutter/test/material/page_test.dart

@@ -282,7 +282,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('PUSH'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => Container(child: const Text('HELLO')),
@@ -737,7 +737,7 @@ void main() {
     expect(homeTapCount, 1);
     expect(pageTapCount, 0);
 
-    final ValueNotifier<bool> notifier = Navigator.of(homeScaffoldKey.currentContext!)!.userGestureInProgressNotifier;
+    final ValueNotifier<bool> notifier = Navigator.of(homeScaffoldKey.currentContext!).userGestureInProgressNotifier;
     expect(notifier.value, false);
 
     Navigator.push<void>(homeScaffoldKey.currentContext!, MaterialPageRoute<void>(

packages/flutter/test/material/page_transitions_theme_test.dart

@@ -26,7 +26,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('push'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => const Text('page b'),
@@ -52,7 +52,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('push'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => const Text('page b'),
@@ -85,7 +85,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('push'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => const Text('page b'),
@@ -125,7 +125,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('push'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => const Text('page b'),
@@ -169,7 +169,7 @@ void main() {
       '/': (BuildContext context) => Material(
         child: TextButton(
           child: const Text('push'),
-          onPressed: () { Navigator.of(context)!.pushNamed('/b'); },
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
         ),
       ),
       '/b': (BuildContext context) => StatefulBuilder(

packages/flutter/test/material/popup_menu_test.dart

@@ -124,7 +124,7 @@ void main() {
     await tester.tap(find.byKey(withCallbackKey));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
-    Navigator.of(popupContext)!.pop();
+    Navigator.of(popupContext).pop();
     await tester.pump();
     expect(cancels, equals(2));
   });

packages/flutter/test/material/range_slider_test.dart

@@ -1372,12 +1372,12 @@ void main() {
                   ElevatedButton(
                     child: const Text('Next'),
                     onPressed: () {
-                      Navigator.of(context)!.pushReplacement(
+                      Navigator.of(context).pushReplacement(
                         MaterialPageRoute<void>(
                           builder: (BuildContext context) {
                             return ElevatedButton(
                               child: const Text('Inner page'),
-                              onPressed: () { Navigator.of(context)!.pop(); },
+                              onPressed: () { Navigator.of(context).pop(); },
                             );
                           },
                         ),

packages/flutter/test/material/slider_test.dart

@@ -2086,12 +2086,12 @@ void main() {
                   ElevatedButton(
                     child: const Text('Next'),
                     onPressed: () {
-                      Navigator.of(context)!.pushReplacement(
+                      Navigator.of(context).pushReplacement(
                         MaterialPageRoute<void>(
                           builder: (BuildContext context) {
                             return ElevatedButton(
                               child: const Text('Inner page'),
-                              onPressed: () { Navigator.of(context)!.pop(); },
+                              onPressed: () { Navigator.of(context).pop(); },
                             );
                           },
                         ),

packages/flutter/test/material/snack_bar_test.dart

@@ -2035,7 +2035,7 @@ void main() {
                   key: transitionTarget,
                   child: const Text('PUSH'),
                   onPressed: () {
-                    Navigator.of(context)!.pushNamed('/second');
+                    Navigator.of(context).pushNamed('/second');
                   },
                 ),
               ),

packages/flutter/test/material/text_field_focus_test.dart

@@ -38,7 +38,7 @@ void main() {
 
     expect(tester.testTextInput.isVisible, isFalse);
 
-    Navigator.of(tester.element(find.text('Dialog')))!.pop();
+    Navigator.of(tester.element(find.text('Dialog'))).pop();
     await tester.pump();
 
     expect(focusNode.hasPrimaryFocus, isTrue);

packages/flutter/test/material/will_pop_test.dart

@@ -139,7 +139,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push(MaterialPageRoute<void>(
+                    Navigator.of(context).push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => Future<bool>.value(willPopValue),
@@ -178,7 +178,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push(MaterialPageRoute<void>(
+                    Navigator.of(context).push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => Future<bool>.value(willPopValue),
@@ -230,11 +230,11 @@ void main() {
             actions: <Widget> [
               TextButton(
                 child: const Text('YES'),
-                onPressed: () { Navigator.of(context)!.pop(true); },
+                onPressed: () { Navigator.of(context).pop(true); },
               ),
               TextButton(
                 child: const Text('NO'),
-                onPressed: () { Navigator.of(context)!.pop(false); },
+                onPressed: () { Navigator.of(context).pop(false); },
               ),
             ],
           );
@@ -252,7 +252,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push(MaterialPageRoute<void>(
+                    Navigator.of(context).push(MaterialPageRoute<void>(
                       builder: (BuildContext context) {
                         return SampleForm(
                           callback: () => showYesNoAlert(context),
@@ -338,7 +338,7 @@ void main() {
                 child: TextButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push(route);
+                    Navigator.of(context).push(route);
                   },
                 ),
               );

packages/flutter/test/widgets/focus_traversal_test.dart

@@ -349,7 +349,7 @@ void main() {
                   focusNode: testNode1,
                   autofocus: true,
                   onPressed: () {
-                    Navigator.of(context)!.push<void>(
+                    Navigator.of(context).push<void>(
                       MaterialPageRoute<void>(
                         builder: (BuildContext context) {
                           return Center(
@@ -358,7 +358,7 @@ void main() {
                               focusNode: testNode2,
                               autofocus: true,
                               onPressed: () {
-                                Navigator.of(context)!.pop();
+                                Navigator.of(context).pop();
                               },
                               child: const Text('Go Back'),
                             ),
@@ -1148,7 +1148,7 @@ void main() {
                     focusNode: testNode1,
                     autofocus: true,
                     onPressed: () {
-                      Navigator.of(context)!.push<void>(
+                      Navigator.of(context).push<void>(
                         MaterialPageRoute<void>(
                           builder: (BuildContext context) {
                             return Center(
@@ -1159,7 +1159,7 @@ void main() {
                                   focusNode: testNode2,
                                   autofocus: true,
                                   onPressed: () {
-                                    Navigator.of(context)!.pop();
+                                    Navigator.of(context).pop();
                                   },
                                   child: const Text('Go Back'),
                                 ),

packages/flutter/test/widgets/inherited_theme_test.dart

@@ -59,7 +59,7 @@ void main() {
                           behavior: HitTestBehavior.opaque,
                           onTap: () {
                             navigatorContext = context;
-                            Navigator.of(context)!.push(
+                            Navigator.of(context).push(
                               TestRoute(
                                 useCaptureAll
                                   ? InheritedTheme.captureAll(context, const IconTextBox('Hello'))
@@ -121,7 +121,7 @@ void main() {
 
     // Return to the home route
     useCaptureAll = true;
-    Navigator.of(navigatorContext)!.pop();
+    Navigator.of(navigatorContext).pop();
     await tester.pumpAndSettle(); // route transition
 
     // Verify that all is the same as it was when the test started

packages/flutter/test/widgets/navigator_test.dart

@@ -204,13 +204,13 @@ void main() {
                         return ElevatedButton(
                           child: const Text('Next'),
                           onPressed: () {
-                            Navigator.of(context)!.push(
+                            Navigator.of(context).push(
                               MaterialPageRoute<void>(
                                 builder: (BuildContext context) {
                                   return ElevatedButton(
                                     child: const Text('Inner page'),
                                     onPressed: () {
-                                      Navigator.of(context, rootNavigator: true)!.push(
+                                      Navigator.of(context, rootNavigator: true).push(
                                         MaterialPageRoute<void>(
                                           builder: (BuildContext context) {
                                             return const Text('Dialog');
@@ -783,8 +783,8 @@ void main() {
       '/A/B': (BuildContext context) => OnTapPage(
         id: 'B',
         onTap: (){
-          Navigator.of(context)!.popUntil((Route<dynamic> route) => route.isFirst);
-          Navigator.of(context)!.pushReplacementNamed('/C');
+          Navigator.of(context).popUntil((Route<dynamic> route) => route.isFirst);
+          Navigator.of(context).pushReplacementNamed('/C');
         },
       ),
       '/C': (BuildContext context) => const OnTapPage(id: 'C',
@@ -851,7 +851,7 @@ void main() {
         id: 'B',
         onTap: (){
           // Pops all routes with bad predicate.
-          Navigator.of(context)!.popUntil((Route<dynamic> route) => false);
+          Navigator.of(context).popUntil((Route<dynamic> route) => false);
         },
       ),
     };
@@ -929,7 +929,7 @@ void main() {
       '/A/B': (BuildContext context) => OnTapPage(
         id: 'B',
         onTap: () {
-          Navigator.of(context)!.pushNamedAndRemoveUntil('/D', ModalRoute.withName('/A'));
+          Navigator.of(context).pushNamedAndRemoveUntil('/D', ModalRoute.withName('/A'));
         },
       ),
       '/D': (BuildContext context) => const Text('page D'),
@@ -1597,7 +1597,7 @@ void main() {
     final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
       '/' : (BuildContext context) => OnTapPage(id: '/', onTap: () {
         Navigator.pushNamed(context, '/A');
-        Navigator.of(context)!.pop();
+        Navigator.of(context).pop();
       }),
       '/A': (BuildContext context) => OnTapPage(id: 'A', onTap: () { Navigator.pop(context); }),
     };
@@ -1825,12 +1825,12 @@ void main() {
   });
 
   testWidgets('initial routes below opaque route are offstage', (WidgetTester tester) async {
-    final GlobalKey<NavigatorState> g = GlobalKey<NavigatorState>();
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
     await tester.pumpWidget(
       Directionality(
         textDirection: TextDirection.ltr,
         child: Navigator(
-          key: g,
+          key: testKey,
           initialRoute: '/a/b',
           onGenerateRoute: (RouteSettings s) {
             return MaterialPageRoute<void>(
@@ -1850,7 +1850,7 @@ void main() {
     expect(find.text('+/a+', skipOffstage: false), findsOneWidget);
     expect(find.text('+/a/b+'), findsOneWidget);
 
-    g.currentState!.pop();
+    testKey.currentState!.pop();
     await tester.pumpAndSettle();
 
     expect(find.text('+/+'), findsNothing);
@@ -1858,7 +1858,7 @@ void main() {
     expect(find.text('+/a+'), findsOneWidget);
     expect(find.text('+/a/b+'), findsNothing);
 
-    g.currentState!.pop();
+    testKey.currentState!.pop();
     await tester.pumpAndSettle();
 
     expect(find.text('+/+'), findsOneWidget);
@@ -1868,12 +1868,12 @@ void main() {
 
   testWidgets('Can provide custom onGenerateInitialRoutes', (WidgetTester tester) async {
     bool onGenerateInitialRoutesCalled = false;
-    final GlobalKey<NavigatorState> g = GlobalKey<NavigatorState>();
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
     await tester.pumpWidget(
       Directionality(
         textDirection: TextDirection.ltr,
         child: Navigator(
-          key: g,
+          key: testKey,
           initialRoute: 'Hello World',
           onGenerateInitialRoutes: (NavigatorState navigator, String initialRoute) {
             onGenerateInitialRoutesCalled = true;
@@ -1893,7 +1893,7 @@ void main() {
     expect(find.text('Hello'), findsNothing);
     expect(find.text('World'), findsOneWidget);
 
-    g.currentState!.pop();
+    testKey.currentState!.pop();
     await tester.pumpAndSettle();
 
     expect(find.text('Hello'), findsOneWidget);
@@ -1901,16 +1901,16 @@ void main() {
   });
 
   testWidgets('Navigator.of able to handle input context is a navigator context', (WidgetTester tester) async {
-    final GlobalKey<NavigatorState> g = GlobalKey<NavigatorState>();
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
     await tester.pumpWidget(
       MaterialApp(
-        navigatorKey: g,
+        navigatorKey: testKey,
         home: const Text('home'),
       )
     );
 
-    final NavigatorState state = Navigator.of(g.currentContext!)!;
-    expect(state, g.currentState);
+    final NavigatorState state = Navigator.of(testKey.currentContext!);
+    expect(state, testKey.currentState);
   });
 
   testWidgets('Navigator.of able to handle input context is a navigator context - root navigator', (WidgetTester tester) async {
@@ -1931,7 +1931,61 @@ void main() {
       )
     );
 
-    final NavigatorState state = Navigator.of(sub.currentContext!, rootNavigator: true)!;
+    final NavigatorState state = Navigator.of(sub.currentContext!, rootNavigator: true);
+    expect(state, root.currentState);
+  });
+
+  testWidgets('Navigator.maybeOf throws when there is no navigator', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
+    await tester.pumpWidget(SizedBox(key: testKey));
+
+    expect(() async {
+      Navigator.of(testKey.currentContext!);
+    }, throwsFlutterError);
+  });
+
+  testWidgets('Navigator.maybeOf works when there is no navigator', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
+    await tester.pumpWidget(SizedBox(key: testKey));
+
+    final NavigatorState? state = Navigator.maybeOf(testKey.currentContext!);
+    expect(state, isNull);
+  });
+
+  testWidgets('Navigator.maybeOf able to handle input context is a navigator context', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> testKey = GlobalKey<NavigatorState>();
+    await tester.pumpWidget(
+        MaterialApp(
+          navigatorKey: testKey,
+          home: const Text('home'),
+        )
+    );
+
+    final NavigatorState? state = Navigator.maybeOf(testKey.currentContext!);
+    expect(state, isNotNull);
+    expect(state, testKey.currentState);
+  });
+
+  testWidgets('Navigator.maybeOf able to handle input context is a navigator context - root navigator', (WidgetTester tester) async {
+    final GlobalKey<NavigatorState> root = GlobalKey<NavigatorState>();
+    final GlobalKey<NavigatorState> sub = GlobalKey<NavigatorState>();
+    await tester.pumpWidget(
+        MaterialApp(
+          navigatorKey: root,
+          home: Navigator(
+            key: sub,
+            onGenerateRoute: (RouteSettings settings) {
+              return MaterialPageRoute<void>(
+                settings: settings,
+                builder: (BuildContext context) => const Text('dummy'),
+              );
+            },
+          ),
+        )
+    );
+
+    final NavigatorState? state = Navigator.maybeOf(sub.currentContext!, rootNavigator: true);
+    expect(state, isNotNull);
     expect(state, root.currentState);
   });
 

packages/flutter/test/widgets/page_route_builder_test.dart

@@ -26,7 +26,7 @@ class HomePage extends StatefulWidget {
 
 class _HomePageState extends State<HomePage> {
   void _presentModalPage() {
-    Navigator.of(context)!.push(PageRouteBuilder<void>(
+    Navigator.of(context).push(PageRouteBuilder<void>(
       transitionDuration: const Duration(milliseconds: 300),
       barrierColor: Colors.black54,
       opaque: false,
@@ -62,7 +62,7 @@ class ModalPage extends StatelessWidget {
               highlightColor: Colors.transparent,
               splashColor: Colors.transparent,
               onTap: () {
-                Navigator.of(context)!.pop();
+                Navigator.of(context).pop();
               },
               child: const SizedBox.expand(),
             ),

packages/flutter/test/widgets/routes_test.dart

@@ -563,7 +563,7 @@ void main() {
               builder: (BuildContext context) {
                 return ElevatedButton(
                   onPressed: () {
-                    Navigator.of(context)!.push<void>(
+                    Navigator.of(context).push<void>(
                       PageRouteBuilder<void>(
                         settings: settings,
                         pageBuilder: (BuildContext context, Animation<double> input, Animation<double> out) {
@@ -612,7 +612,7 @@ void main() {
             builder: (BuildContext context) {
               return ElevatedButton(
                 onPressed: () {
-                  Navigator.of(context)!.push<void>(
+                  Navigator.of(context).push<void>(
                     PageRouteBuilder<void>(
                       settings: settings,
                       pageBuilder: (BuildContext context, Animation<double> input, Animation<double> out) {
@@ -1138,7 +1138,7 @@ void main() {
             builder: (BuildContext context) {
               return ElevatedButton(
                 onPressed: () {
-                  Navigator.of(context)!.push<void>(
+                  Navigator.of(context).push<void>(
                     MaterialPageRoute<void>(
                       builder: (BuildContext innerContext) {
                         return Container(
@@ -1188,7 +1188,7 @@ void main() {
             builder: (BuildContext context) {
               return ElevatedButton(
                 onPressed: () {
-                  Navigator.of(context)!.push<void>(
+                  Navigator.of(context).push<void>(
                     ModifiedReverseTransitionDurationRoute<void>(
                       builder: (BuildContext innerContext) {
                         return Container(
@@ -1247,7 +1247,7 @@ void main() {
             builder: (BuildContext context) {
               return ElevatedButton(
                 onPressed: () {
-                  Navigator.of(context)!.push<void>(
+                  Navigator.of(context).push<void>(
                     ModifiedReverseTransitionDurationRoute<void>(
                       builder: (BuildContext innerContext) {
                         return Container(
@@ -1309,7 +1309,7 @@ void main() {
                 child: ElevatedButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push<void>(
+                    Navigator.of(context).push<void>(
                       _TestDialogRouteWithCustomBarrierCurve<void>(
                         child: const Text('Hello World'),
                       )
@@ -1371,7 +1371,7 @@ void main() {
                 child: ElevatedButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push<void>(
+                    Navigator.of(context).push<void>(
                       _TestDialogRouteWithCustomBarrierCurve<void>(
                         child: const Text('Hello World'),
                         barrierCurve: Curves.linear,
@@ -1436,7 +1436,7 @@ void main() {
                 child: ElevatedButton(
                   child: const Text('X'),
                   onPressed: () {
-                    Navigator.of(context)!.push<void>(
+                    Navigator.of(context).push<void>(
                       _TestDialogRouteWithCustomBarrierCurve<void>(
                         child: const Text('Hello World'),
                         barrierLabel: 'test label',