update to flutter 2.12.0

loc_chain_app/lib/pages/home.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 
 class HomePage extends StatefulWidget {
-  HomePage({Key key, this.title}) : super(key: key);
+  HomePage({Key? key, required this.title}) : super(key: key);
   final String title;
 
   @override

loc_chain_app/lib/pages/keygen.dart

@@ -51,7 +51,7 @@ class KeyFileManager {
 }
 
 class KeygenPage extends StatefulWidget {
-  KeygenPage({Key key, this.title}) : super(key: key);
+  KeygenPage({Key? key, required this.title}) : super(key: key);
   final String title;
 
   @override

loc_chain_app/lib/widgets/navbar.dart

@@ -3,7 +3,7 @@ import 'package:loc_chain_app/pages/home.dart';
 import 'package:loc_chain_app/pages/keygen.dart';
 
 class NavBarWidget extends StatefulWidget {
-  NavBarWidget({Key key}) : super(key: key);
+  NavBarWidget({Key? key}) : super(key: key);
 
   @override
   _NavBarWidgetState createState() => _NavBarWidgetState();
@@ -11,7 +11,7 @@ class NavBarWidget extends StatefulWidget {
 
 class _NavBarWidgetState extends State<NavBarWidget> {
   int _selectedIndex = 0;
-  StatefulWidget _selectedWidget;
+  Widget _selectedWidget = HomePage(title: 'Home');
   static List<Widget> pages = <Widget>[
     HomePage(
       title: 'Home',

loc_chain_app/pubspec.lock

@@ -267,5 +267,5 @@ packages:
     source: hosted
     version: "0.1.2"
 sdks:
-  dart: ">=2.12.0-0.0 <3.0.0"
+  dart: ">=2.12.0 <3.0.0"
   flutter: ">=1.12.13+hotfix.5"

loc_chain_app/pubspec.yaml

@@ -18,7 +18,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter: