Migrate some widgets to null safety

lib/widgets/pro_overlay.dart

@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:flutter/material.dart';
 
 import 'package:easy_localization/easy_localization.dart';
@@ -13,7 +11,7 @@ class ProOverlay extends StatelessWidget {
   final Widget child;
   final Feature feature;
 
-  ProOverlay({@required this.child, @required this.feature}) {
+  ProOverlay({required this.child, required this.feature}) {
     assert(feature.pro == true);
   }
 

lib/widgets/rename_dialog.dart

@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'dart:io';
 
 import 'package:flutter/material.dart';
@@ -14,9 +12,9 @@ class RenameDialog extends StatefulWidget {
   final String dialogTitle;
 
   RenameDialog({
-    @required this.oldPath,
-    @required this.inputDecoration,
-    @required this.dialogTitle,
+    required this.oldPath,
+    required this.inputDecoration,
+    required this.dialogTitle,
   });
 
   @override
@@ -24,7 +22,7 @@ class RenameDialog extends StatefulWidget {
 }
 
 class _RenameDialogState extends State<RenameDialog> {
-  TextEditingController _textController;
+  late TextEditingController _textController;
   final _formKey = GlobalKey<FormState>();
 
   @override
@@ -43,7 +41,7 @@ class _RenameDialogState extends State<RenameDialog> {
           TextFormField(
             decoration: InputDecoration(labelText: widget.inputDecoration),
             validator: (value) {
-              if (value.isEmpty) {
+              if (value!.isEmpty) {
                 return tr('widgets.rename.validator.empty');
               }
 
@@ -76,7 +74,7 @@ class _RenameDialogState extends State<RenameDialog> {
         ),
         TextButton(
           onPressed: () {
-            if (_formKey.currentState.validate()) {
+            if (_formKey.currentState!.validate()) {
               var newName = _textController.text;
               Navigator.of(context).pop(newName);
             }

lib/widgets/sorting_mode_selector.dart

@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:flutter/material.dart';
 
 import 'package:easy_localization/easy_localization.dart';
@@ -17,8 +15,8 @@ class SortingModeSelector extends StatefulWidget {
 }
 
 class _SortingModeSelectorState extends State<SortingModeSelector> {
-  SortingField field;
-  SortingOrder order;
+  late SortingField field;
+  late SortingOrder order;
 
   @override
   void initState() {
@@ -68,9 +66,9 @@ class _SortingModeSelectorState extends State<SortingModeSelector> {
       title: Text(sf.toPublicString()),
       value: sf,
       groupValue: field,
-      onChanged: (SortingField sf) {
+      onChanged: (SortingField? sf) {
         setState(() {
-          field = sf;
+          field = sf!;
         });
       },
     );
@@ -81,9 +79,9 @@ class _SortingModeSelectorState extends State<SortingModeSelector> {
       title: Text(so.toPublicString()),
       value: so,
       groupValue: order,
-      onChanged: (SortingOrder so) {
+      onChanged: (SortingOrder? so) {
         setState(() {
-          order = so;
+          order = so!;
         });
       },
     );

lib/widgets/sync_button.dart

@@ -1,4 +1,4 @@
-// @dart=2.9
+
 
 import 'dart:async';
 
@@ -19,8 +19,8 @@ class SyncButton extends StatefulWidget {
 }
 
 class _SyncButtonState extends State<SyncButton> {
-  StreamSubscription<ConnectivityResult> subscription;
-  ConnectivityResult _connectivity;
+  late StreamSubscription<ConnectivityResult> subscription;
+  ConnectivityResult? _connectivity;
 
   @override
   void initState() {
@@ -126,7 +126,7 @@ class BlinkingIcon extends StatefulWidget {
   final Widget child;
   final int interval;
 
-  BlinkingIcon({@required this.child, this.interval = 500, Key key})
+  BlinkingIcon({required this.child, this.interval = 500, Key? key})
       : super(key: key);
 
   @override
@@ -135,8 +135,8 @@ class BlinkingIcon extends StatefulWidget {
 
 class _BlinkingIconState extends State<BlinkingIcon>
     with SingleTickerProviderStateMixin {
-  AnimationController _controller;
-  Animation<double> _animation;
+  late AnimationController _controller;
+  late Animation<double> _animation;
 
   @override
   void initState() {
@@ -172,13 +172,13 @@ class _BlinkingIconState extends State<BlinkingIcon>
 class GitPendingChangesBadge extends StatelessWidget {
   final Widget child;
 
-  GitPendingChangesBadge({@required this.child});
+  GitPendingChangesBadge({required this.child});
 
   @override
   Widget build(BuildContext context) {
     var theme = Theme.of(context);
     var darkMode = theme.brightness == Brightness.dark;
-    var style = theme.textTheme.caption.copyWith(
+    var style = theme.textTheme.caption!.copyWith(
       fontSize: 6.0,
       color: darkMode ? Colors.black : Colors.white,
     );
@@ -188,7 +188,7 @@ class GitPendingChangesBadge extends StatelessWidget {
     return Badge(
       badgeContent: Text(repo.numChanges.toString(), style: style),
       showBadge: repo.numChanges != 0,
-      badgeColor: theme.iconTheme.color,
+      badgeColor: theme.iconTheme.color!,
       position: BadgePosition.topEnd(top: 10.0, end: 4.0),
       child: child,
     );