Migrate flavors to null safety (#80558)

dev/integration_tests/flavors/lib/main.dart

@@ -12,19 +12,19 @@ void main() {
 }
 
 class Flavor extends StatefulWidget {
-  const Flavor({Key key}) : super(key: key);
+  const Flavor({Key? key}) : super(key: key);
 
   @override
   _FlavorState createState() => _FlavorState();
 }
 
 class _FlavorState extends State<Flavor> {
-  String _flavor;
+  String? _flavor;
 
   @override
   void initState() {
     super.initState();
-    const MethodChannel('flavor').invokeMethod<String>('getFlavor').then((String flavor) {
+    const MethodChannel('flavor').invokeMethod<String>('getFlavor').then((String? flavor) {
       setState(() {
         _flavor = flavor;
       });
@@ -37,7 +37,7 @@ class _FlavorState extends State<Flavor> {
       textDirection: TextDirection.ltr,
       child: _flavor == null
         ? const Text('Awaiting flavor...')
-        : Text(_flavor, key: const ValueKey<String>('flavor')),
+        : Text(_flavor!, key: const ValueKey<String>('flavor')),
     );
   }
 }

dev/integration_tests/flavors/pubspec.yaml

@@ -2,7 +2,7 @@ name: flavors
 description: Integration test for build flavors.
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
   flutter:

dev/integration_tests/flavors/test_driver/main_test.dart

@@ -7,7 +7,7 @@ import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
 
 void main() {
   group('flavors suite', () {
-    FlutterDriver driver;
+    late FlutterDriver driver;
 
     setUpAll(() async {
       driver = await FlutterDriver.connect();
@@ -20,7 +20,7 @@ void main() {
     });
 
     tearDownAll(() async {
-      driver?.close();
+      driver.close();
     });
   });
 }