added backward compability (Flutter 3)

 typedef ValueUpdater<T> = T Function();
+
+T? ambiguate<T>(T? value) => value;

 import 'package:flutter/foundation.dart';
 import 'package:flutter/scheduler.dart';
 
+import '../../get.dart';
+
 /// The [GetLifeCycle]
 ///
 /// ```dart
@@ -16,7 +18,8 @@ mixin GetLifeCycleMixin {
   @protected
   @mustCallSuper
   void onInit() {
-    SchedulerBinding.instance?.addPostFrameCallback((_) => onReady());
+    ambiguate(SchedulerBinding.instance)
+        ?.addPostFrameCallback((_) => onReady());
   }
 
   /// Called 1 frame after onInit(). It is the perfect place to enter

@@ -358,7 +358,7 @@ extension ExtensionSnackbar on GetInterface {
     if (instantInit) {
       controller.show();
     } else {
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      ambiguate(SchedulerBinding.instance)!.addPostFrameCallback((_) {
         controller.show();
       });
     }
@@ -469,7 +469,7 @@ extension ExtensionSnackbar on GetInterface {
       controller.show();
     } else {
       //routing.isSnackbar = true;
-      SchedulerBinding.instance!.addPostFrameCallback((_) {
+      ambiguate(SchedulerBinding.instance)!.addPostFrameCallback((_) {
         controller.show();
       });
     }

@@ -52,7 +52,7 @@ class RouterReportManager<T> {
 
   void reportRouteDispose(T disposed) {
     if (Get.smartManagement != SmartManagement.onlyBuilder) {
-      WidgetsBinding.instance!.addPostFrameCallback((_) {
+      ambiguate(WidgetsBinding.instance)!.addPostFrameCallback((_) {
         _removeDependencyByRoute(disposed);
       });
     }

@@ -449,7 +449,7 @@ You need to either use message[String], or messageText[Widget] or define a userI
   }
 
   void _configureLeftBarFuture() {
-    SchedulerBinding.instance!.addPostFrameCallback(
+    ambiguate(SchedulerBinding.instance)!.addPostFrameCallback(
       (_) {
         final keyContext = _backgroundBoxKey.currentContext;
         if (keyContext != null) {

@@ -96,13 +96,13 @@ mixin FullLifeCycleMixin on FullLifeCycleController {
   @override
   void onInit() {
     super.onInit();
-    WidgetsBinding.instance!.addObserver(this);
+    ambiguate(WidgetsBinding.instance)!.addObserver(this);
   }
 
   @mustCallSuper
   @override
   void onClose() {
-    WidgetsBinding.instance!.removeObserver(this);
+    ambiguate(WidgetsBinding.instance)!.removeObserver(this);
     super.onClose();
   }
 

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
 
+import '../../../get_core/src/typedefs.dart';
 import 'list_notifier.dart';
 
 typedef ValueBuilderUpdateCallback<T> = void Function(T snapshot);
@@ -102,13 +103,14 @@ mixin ObserverComponent on ComponentElement {
 
   Future<bool> _safeRebuild() async {
     if (dirty) return false;
-    if (SchedulerBinding.instance == null) {
+    if (ambiguate(SchedulerBinding.instance) == null) {
       markNeedsBuild();
     } else {
       // refresh was called during the building
-      if (SchedulerBinding.instance!.schedulerPhase != SchedulerPhase.idle) {
+      if (ambiguate(SchedulerBinding.instance)!.schedulerPhase 
+      != SchedulerPhase.idle) {
         // Await for the end of build
-        await SchedulerBinding.instance!.endOfFrame;
+        await ambiguate(SchedulerBinding.instance)!.endOfFrame;
         if (dirty) return false;
       }