chore: update null safety

Author: DonsWayo

example/lib/main.dart

@@ -8,24 +8,22 @@ class MyApp extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return MaterialApp(
-      title: 'Flutter Demo',
-      theme: ThemeData(
-        primarySwatch: Colors.blue,
-      ),
-      home: HomePage()
-    );
+        title: 'Flutter Demo',
+        theme: ThemeData(
+          primarySwatch: Colors.blue,
+        ),
+        home: HomePage());
   }
 }
 
 class HomePage extends StatefulWidget {
-  HomePage({Key key}) : super(key: key);
+  HomePage({Key? key}) : super(key: key);
 
   @override
   _HomePageState createState() => _HomePageState();
 }
 
 class _HomePageState extends State<HomePage> {
-
   final ScrollController scrollController = ScrollController();
   final List<String> entries = <String>[
     'A',
@@ -59,9 +57,10 @@ class _HomePageState extends State<HomePage> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      body: Stack(
-        children: <Widget>[listDemo(), FluentAppBar(scrollController: scrollController, titleText: 'Home')]
-      ),
+      body: Stack(children: <Widget>[
+        listDemo(),
+        FluentAppBar(scrollController: scrollController, titleText: 'Home')
+      ]),
     );
   }
 

example/pubspec.yaml

@@ -14,7 +14,7 @@ description: A new Flutter project.
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:

lib/fluent_appbar.dart

@@ -4,9 +4,9 @@ import 'package:flutter/material.dart';
 
 class FluentAppBar extends StatefulWidget {
   FluentAppBar({
-    Key key,
-    @required this.titleText,
-    @required this.scrollController,
+    Key? key,
+    required this.titleText,
+    required this.scrollController,
     this.scrollOffset = 34,
     this.appBarColor = Colors.white,
     this.boxShadowColor = Colors.black,
@@ -29,8 +29,8 @@ class FluentAppBar extends StatefulWidget {
 class _FluentAppBarState extends State<FluentAppBar>
     with TickerProviderStateMixin {
   double topBarOpacity = 0.0;
-  Animation<double> topBarAnimation;
-  AnimationController animationController;
+  late Animation<double> topBarAnimation;
+  late AnimationController animationController;
 
   @override
   void initState() {
@@ -85,7 +85,7 @@ class _FluentAppBarState extends State<FluentAppBar>
       children: <Widget>[
         AnimatedBuilder(
           animation: animationController,
-          builder: (BuildContext context, Widget child) {
+          builder: (BuildContext context, Widget? child) {
             return FadeTransition(
               opacity: topBarAnimation,
               child: Transform(

pubspec.yaml

@@ -4,7 +4,7 @@ version: 1.0.0
 homepage: https://github.com/DonsWayo/fluent_appbar
 
 environment:
-  sdk: ">=2.1.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter: