Implemented Null Safety.

example/lib/main.dart

@@ -22,7 +22,7 @@ class MyApp extends StatelessWidget {
 class LoginPage extends StatefulWidget {
   final VoidCallback _onSignIn;
 
-  LoginPage({@required onSignIn})
+  LoginPage({required onSignIn})
       : assert(onSignIn != null),
         _onSignIn = onSignIn;
 
@@ -40,13 +40,13 @@ class _LoginPageState extends State<LoginPage> {
   bool _isInvalidAsyncUser = false; // managed after response from server
   bool _isInvalidAsyncPass = false; // managed after response from server
 
-  String _username;
-  String _password;
+  String? _username;
+  String? _password;
   bool _isLoggedIn = false;
 
   // validate user name
-  String _validateUserName(String userName) {
-    if (userName.length < 8) {
+  String? _validateUserName(String? userName) {
+    if (userName!.length < 8) {
       return 'Username must be at least 8 characters';
     }
 
@@ -60,8 +60,8 @@ class _LoginPageState extends State<LoginPage> {
   }
 
   // validate password
-  String _validatePassword(String password) {
-    if (password.length < 8) {
+  String? _validatePassword(String? password) {
+    if (password!.length < 8) {
       return 'Password must be at least 8 characters';
     }
 
@@ -75,8 +75,8 @@ class _LoginPageState extends State<LoginPage> {
   }
 
   void _submit() {
-    if (_loginFormKey.currentState.validate()) {
-      _loginFormKey.currentState.save();
+    if (_loginFormKey.currentState!.validate()) {
+      _loginFormKey.currentState!.save();
 
       // dismiss keyboard during async call
       FocusScope.of(context).requestFocus(new FocusNode());
@@ -154,7 +154,7 @@ class _LoginPageState extends State<LoginPage> {
               key: Key('username'),
               decoration: InputDecoration(
                   hintText: 'enter username', labelText: 'User Name'),
-              style: TextStyle(fontSize: 20.0, color: textTheme.button.color),
+              style: TextStyle(fontSize: 20.0, color: textTheme.button!.color),
               validator: _validateUserName,
               onSaved: (value) => _username = value,
             ),
@@ -166,7 +166,7 @@ class _LoginPageState extends State<LoginPage> {
               obscureText: true,
               decoration: InputDecoration(
                   hintText: 'enter password', labelText: 'Password'),
-              style: TextStyle(fontSize: 20.0, color: textTheme.button.color),
+              style: TextStyle(fontSize: 20.0, color: textTheme.button!.color),
               validator: _validatePassword,
               onSaved: (value) => _password = value,
             ),

example/pubspec.lock

@@ -157,5 +157,5 @@ packages:
     source: hosted
     version: "2.1.0"
 sdks:
-  dart: ">=2.12.0-0.0 <3.0.0"
+  dart: ">=2.12.0 <3.0.0"
   flutter: ">=1.20.0"

example/pubspec.yaml

@@ -6,7 +6,7 @@ description: Demonstrates how to use the modal_progress_hud_nsn plugin.
 publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   flutter:

example/test/widget_test.dart

@@ -19,7 +19,7 @@ void main() {
     expect(
       find.byWidgetPredicate(
         (Widget widget) => widget is Text &&
-                           widget.data.startsWith('Running on:'),
+                           widget.data!.startsWith('Running on:'),
       ),
       findsOneWidget,
     );