Add null return statements to nullable functions with implicit returns (#94760)

packages/flutter/lib/src/services/restoration.dart

@@ -304,7 +304,7 @@ class RestorationManager extends ChangeNotifier {
     );
   }
 
-  Future<Object?> _methodHandler(MethodCall call) async {
+  Future<void> _methodHandler(MethodCall call) async {
     switch (call.method) {
       case 'push':
         _parseAndHandleRestorationUpdateFromEngine(call.arguments as Map<Object?, Object?>);

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

@@ -1489,7 +1489,7 @@ class PrioritizedAction extends Action<PrioritizedIntents> {
   }
 
   @override
-  Object? invoke(PrioritizedIntents intent) {
+  void invoke(PrioritizedIntents intent) {
     assert(_selectedAction != null);
     assert(_selectedIntent != null);
     _selectedAction.invoke(_selectedIntent);

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

@@ -3741,13 +3741,13 @@ class _UpdateTextSelectionToAdjacentLineAction<T extends DirectionalCaretMovemen
   }
 
   @override
-  Object? invoke(T intent, [BuildContext? context]) {
+  void invoke(T intent, [BuildContext? context]) {
     assert(state._value.selection.isValid);
 
     final bool collapseSelection = intent.collapseSelection || !state.widget.selectionEnabled;
     final TextEditingValue value = state._textEditingValueforTextLayoutMetrics;
     if (!value.selection.isValid) {
-      return null;
+      return;
     }
 
     if (_verticalMovementRun?.isValid == false) {
@@ -3807,7 +3807,7 @@ class _CopySelectionAction extends ContextAction<CopySelectionTextIntent> {
   final EditableTextState state;
 
   @override
-  Object? invoke(CopySelectionTextIntent intent, [BuildContext? context]) {
+  void invoke(CopySelectionTextIntent intent, [BuildContext? context]) {
     if (intent.collapseSelection) {
       state.cutSelection(intent.cause);
     } else {

packages/flutter/test/material/checkbox_test.dart

@@ -1077,6 +1077,7 @@ void main() {
         }
         return inactivePressedOverlayColor;
       }
+      return null;
     }
     const double splashRadius = 24.0;
     TestGesture gesture;

packages/flutter/test/rendering/rendering_tester.dart

@@ -305,6 +305,7 @@ class TestClipPaintingContext extends PaintingContext {
     ClipRectLayer? oldLayer,
   }) {
     this.clipBehavior = clipBehavior;
+    return null;
   }
 
   Clip clipBehavior = Clip.none;

packages/flutter/test/widgets/actions_test.dart

@@ -1701,9 +1701,8 @@ class TestContextAction extends ContextAction<TestIntent> {
   List<BuildContext?> capturedContexts = <BuildContext?>[];
 
   @override
-  Object? invoke(covariant TestIntent intent, [BuildContext? context]) {
+  void invoke(covariant TestIntent intent, [BuildContext? context]) {
     capturedContexts.add(context);
-    return null;
   }
 }
 
@@ -1724,7 +1723,7 @@ class LogInvocationAction extends Action<LogIntent> {
   bool get isActionEnabled => enabled;
 
   @override
-  Object? invoke(LogIntent intent) {
+  void invoke(LogIntent intent) {
     final Action<LogIntent>? callingAction = this.callingAction;
     if (callingAction == null) {
       intent.log.add('$actionName.invoke');
@@ -1755,7 +1754,7 @@ class LogInvocationContextAction extends ContextAction<LogIntent> {
   bool get isActionEnabled => enabled;
 
   @override
-  Object? invoke(LogIntent intent, [BuildContext? context]) {
+  void invoke(LogIntent intent, [BuildContext? context]) {
     invokeContext = context;
     final Action<LogIntent>? callingAction = this.callingAction;
     if (callingAction == null) {
@@ -1792,5 +1791,5 @@ class RedirectOutputAction extends LogInvocationAction {
   final List<String> newLog;
 
   @override
-  Object? invoke(LogIntent intent) => super.invoke(LogIntent(log: newLog));
+  void invoke(LogIntent intent) => super.invoke(LogIntent(log: newLog));
 }

packages/flutter/test/widgets/clipboard_utils.dart

@@ -29,5 +29,6 @@ class MockClipboard {
         _clipboardData = methodCall.arguments;
         break;
     }
+    return null;
   }
 }

packages/flutter/test/widgets/router_test.dart

@@ -792,6 +792,7 @@ testWidgets('ChildBackButtonDispatcher take priority recursively', (WidgetTester
         SystemChannels.navigation,
         (MethodCall methodCall) async {
           log.add(methodCall);
+	  return null;
         }
       );
     final RouteInformationProvider provider = PlatformRouteInformationProvider(

packages/flutter/test/widgets/shortcuts_test.dart

@@ -103,6 +103,7 @@ Widget activatorTester(
       if (hasSecond)
         TestIntent2: TestAction(onInvoke: (Intent intent) {
           onInvoke2(intent);
+	  return null;
         }),
     },
     child: Shortcuts(

packages/flutter/test/widgets/slotted_render_object_widget_test.dart

@@ -212,7 +212,7 @@ class _Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWid
   Iterable<_DiagonalSlot> get slots => _DiagonalSlot.values;
 
   @override
-  Widget? childForSlot(Object slot) {
+  Widget? childForSlot(_DiagonalSlot slot) {
     switch (slot) {
       case _DiagonalSlot.topLeft:
         return topLeft;

packages/flutter/test/widgets/title_test.dart

@@ -38,6 +38,7 @@ void main() {
 
     tester.binding.defaultBinaryMessenger.setMockMethodCallHandler(SystemChannels.platform, (MethodCall methodCall) async {
       log.add(methodCall);
+      return null;
     });
 
     await tester.pumpWidget(Title(