refactor: Migrate to null safety

lib/pages/new_private_chat/new_private_chat.dart

@@ -11,7 +11,7 @@ import 'package:fluffychat/utils/url_launcher.dart';
 import 'package:fluffychat/widgets/matrix.dart';
 
 class NewPrivateChat extends StatefulWidget {
-  const NewPrivateChat({Key key}) : super(key: key);
+  const NewPrivateChat({Key? key}) : super(key: key);
 
   @override
   NewPrivateChatController createState() => NewPrivateChatController();
@@ -48,20 +48,20 @@ class NewPrivateChatController extends State<NewPrivateChat> {
 
   void submitAction([_]) async {
     controller.text = controller.text.trim();
-    if (!formKey.currentState.validate()) return;
+    if (!formKey.currentState!.validate()) return;
     UrlLauncher(context, '$prefix${controller.text}').openMatrixToUrl();
   }
 
-  String validateForm(String value) {
-    if (value.isEmpty) {
-      return L10n.of(context).pleaseEnterAMatrixIdentifier;
+  String? validateForm(String? value) {
+    if (value!.isEmpty) {
+      return L10n.of(context)!.pleaseEnterAMatrixIdentifier;
     }
     if (!controller.text.isValidMatrixId ||
         !supportedSigils.contains(controller.text.sigil)) {
-      return L10n.of(context).makeSureTheIdentifierIsValid;
+      return L10n.of(context)!.makeSureTheIdentifierIsValid;
     }
     if (controller.text == Matrix.of(context).client.userID) {
-      return L10n.of(context).youCannotInviteYourself;
+      return L10n.of(context)!.youCannotInviteYourself;
     }
     return null;
   }

lib/pages/new_private_chat/new_private_chat_view.dart

@@ -15,7 +15,7 @@ import 'package:fluffychat/widgets/matrix.dart';
 class NewPrivateChatView extends StatelessWidget {
   final NewPrivateChatController controller;
 
-  const NewPrivateChatView(this.controller, {Key key}) : super(key: key);
+  const NewPrivateChatView(this.controller, {Key? key}) : super(key: key);
 
   static const double _qrCodePadding = 8;
 
@@ -24,13 +24,13 @@ class NewPrivateChatView extends StatelessWidget {
     return Scaffold(
       appBar: AppBar(
         leading: const BackButton(),
-        title: Text(L10n.of(context).newChat),
+        title: Text(L10n.of(context)!.newChat),
         backgroundColor: Theme.of(context).scaffoldBackgroundColor,
         actions: [
           TextButton(
             onPressed: () => VRouter.of(context).to('/newgroup'),
             child: Text(
-              L10n.of(context).createNewGroup,
+              L10n.of(context)!.createNewGroup,
               style: TextStyle(color: Theme.of(context).colorScheme.secondary),
             ),
           )
@@ -67,7 +67,7 @@ class NewPrivateChatView extends StatelessWidget {
               ),
             ),
             ListTile(
-              subtitle: Text(L10n.of(context).createNewChatExplaination),
+              subtitle: Text(L10n.of(context)!.createNewChatExplaination),
             ),
             Padding(
               padding: const EdgeInsets.all(12),
@@ -81,7 +81,7 @@ class NewPrivateChatView extends StatelessWidget {
                   onFieldSubmitted: controller.submitAction,
                   validator: controller.validateForm,
                   decoration: InputDecoration(
-                    labelText: L10n.of(context).typeInInviteLinkManually,
+                    labelText: L10n.of(context)!.typeInInviteLinkManually,
                     hintText: '@username',
                     prefixText: 'matrix.to/#/',
                     suffixIcon: IconButton(
@@ -105,7 +105,7 @@ class NewPrivateChatView extends StatelessWidget {
       floatingActionButton: PlatformInfos.isMobile && !controller.hideFab
           ? FloatingActionButton.extended(
               onPressed: controller.openScannerAction,
-              label: Text(L10n.of(context).scanQrCode),
+              label: Text(L10n.of(context)!.scanQrCode),
               icon: const Icon(Icons.camera_alt_outlined),
             )
           : null,

lib/pages/new_private_chat/qr_scanner_modal.dart

@@ -9,7 +9,7 @@ import 'package:qr_code_scanner/qr_code_scanner.dart';
 import 'package:fluffychat/utils/url_launcher.dart';
 
 class QrScannerModal extends StatefulWidget {
-  const QrScannerModal({Key key}) : super(key: key);
+  const QrScannerModal({Key? key}) : super(key: key);
 
   @override
   _QrScannerModalState createState() => _QrScannerModalState();
@@ -17,15 +17,15 @@ class QrScannerModal extends StatefulWidget {
 
 class _QrScannerModalState extends State<QrScannerModal> {
   final GlobalKey qrKey = GlobalKey(debugLabel: 'QR');
-  QRViewController controller;
+  QRViewController? controller;
 
   @override
   void reassemble() {
     super.reassemble();
     if (Platform.isAndroid) {
-      controller.pauseCamera();
+      controller!.pauseCamera();
     } else if (Platform.isIOS) {
-      controller.resumeCamera();
+      controller!.resumeCamera();
     }
   }
 
@@ -36,9 +36,9 @@ class _QrScannerModalState extends State<QrScannerModal> {
         leading: IconButton(
           icon: const Icon(Icons.close_outlined),
           onPressed: Navigator.of(context).pop,
-          tooltip: L10n.of(context).close,
+          tooltip: L10n.of(context)!.close,
         ),
-        title: Text(L10n.of(context).scanQrCode),
+        title: Text(L10n.of(context)!.scanQrCode),
       ),
       body: Stack(
         children: [
@@ -59,7 +59,7 @@ class _QrScannerModalState extends State<QrScannerModal> {
 
   void _onQRViewCreated(QRViewController controller) {
     this.controller = controller;
-    StreamSubscription sub;
+    late StreamSubscription sub;
     sub = controller.scannedDataStream.listen((scanData) {
       sub.cancel();
       Navigator.of(context).pop();