diff --git a/lib/models/github.dart b/lib/models/github.dart
index 8737fc8..2fde15b 100644
--- a/lib/models/github.dart
+++ b/lib/models/github.dart
@@ -166,7 +166,7 @@ class GithubNotificationItemSubject {
   int? _number;
   int? get number {
     if (_number == null) {
-      _number = int.parse(url?.split('/')?.last ?? '0');
+      _number = int.parse(url?.split('/').last ?? '0');
     }
     return _number;
   }
diff --git a/lib/scaffolds/long_list.dart b/lib/scaffolds/long_list.dart
index e858a93..081e78f 100644
--- a/lib/scaffolds/long_list.dart
+++ b/lib/scaffolds/long_list.dart
@@ -9,17 +9,17 @@ import '../widgets/link.dart';
 import '../widgets/error_reload.dart';
 
 class LongListPayload<T, K> {
-  T? header;
-  int? totalCount;
-  String? cursor;
-  List<K>? leadingItems;
+  T header;
+  int totalCount;
+  String cursor;
+  List<K> leadingItems;
   List<K>? trailingItems;
 
   LongListPayload({
-    this.header,
-    this.totalCount,
-    this.cursor,
-    this.leadingItems,
+    required this.header,
+    required this.totalCount,
+    required this.cursor,
+    required this.leadingItems,
     this.trailingItems,
   });
 }
@@ -51,12 +51,12 @@ class LongListStatefulScaffold<T, K> extends StatefulWidget {
 }
 
 class _LongListStatefulScaffoldState<T, K>
-    extends State<LongListStatefulScaffold<T?, K>> {
+    extends State<LongListStatefulScaffold<T, K>> {
   late bool loading;
   bool loadingMore = false;
   String error = '';
 
-  LongListPayload<T?, K>? payload;
+  LongListPayload<T, K>? payload;
 
   @override
   void initState() {
@@ -94,7 +94,7 @@ class _LongListStatefulScaffoldState<T, K>
           await widget.onLoadMore(payload!.cursor);
       payload!.totalCount = _payload.totalCount;
       payload!.cursor = _payload.cursor;
-      payload!.leadingItems!.addAll(_payload.leadingItems!);
+      payload!.leadingItems.addAll(_payload.leadingItems);
     } finally {
       if (mounted) {
         setState(() {
@@ -113,11 +113,11 @@ class _LongListStatefulScaffoldState<T, K>
 
     int realIndex = index ~/ 2;
 
-    if (realIndex < payload!.leadingItems!.length) {
-      return widget.itemBuilder(payload!.leadingItems![realIndex]);
-    } else if (realIndex == payload!.leadingItems!.length) {
-      var count = payload!.totalCount! -
-          payload!.leadingItems!.length +
+    if (realIndex < payload!.leadingItems.length) {
+      return widget.itemBuilder(payload!.leadingItems[realIndex]);
+    } else if (realIndex == payload!.leadingItems.length) {
+      var count = payload!.totalCount -
+          payload!.leadingItems.length +
           payload!.trailingItems!.length;
       return Container(
         padding: CommonStyle.padding,
@@ -150,13 +150,13 @@ class _LongListStatefulScaffoldState<T, K>
       );
     } else {
       return widget.itemBuilder(payload!
-          .trailingItems![realIndex - payload!.leadingItems!.length - 1]);
+          .trailingItems![realIndex - payload!.leadingItems.length - 1]);
     }
   }
 
   int get _itemCount {
-    int count = payload!.leadingItems!.length + payload!.trailingItems!.length;
-    if (payload!.totalCount! > count) {
+    int count = payload!.leadingItems.length + payload!.trailingItems!.length;
+    if (payload!.totalCount > count) {
       count++;
     }
     return 2 * count; // including bottom border
diff --git a/lib/screens/ge_search.dart b/lib/screens/ge_search.dart
index 0c14b68..9c85013 100644
--- a/lib/screens/ge_search.dart
+++ b/lib/screens/ge_search.dart
@@ -25,7 +25,7 @@ class _GeSearchScreenState extends State<GeSearchScreen> {
   List<List> _payloads = [[], [], []];
 
   TextEditingController? _controller;
-  String get _keyword => _controller!.text?.trim() ?? '';
+  String get _keyword => _controller!.text.trim();
 
   @override
   void initState() {
diff --git a/lib/screens/gh_issue.dart b/lib/screens/gh_issue.dart
index 6d757d3..d4ce060 100644
--- a/lib/screens/gh_issue.dart
+++ b/lib/screens/gh_issue.dart
@@ -87,7 +87,7 @@ class GhIssueScreen extends StatelessWidget {
     );
   }
 
-  Future<GIssueData_repository?> _queryIssue(BuildContext context,
+  Future<GIssueData_repository> _queryIssue(BuildContext context,
       {String? cursor}) async {
     final req = GIssueReq((b) {
       b.vars.owner = owner;
@@ -97,7 +97,7 @@ class GhIssueScreen extends StatelessWidget {
     });
     OperationResponse<GIssueData, GIssueVars?> res =
         await context.read<AuthModel>().gqlClient!.request(req).first;
-    return res.data!.repository;
+    return res.data!.repository!;
   }
 
   @override
@@ -257,15 +257,14 @@ class GhIssueScreen extends StatelessWidget {
       },
       itemBuilder: (p) => TimelineItem(p),
       onRefresh: () async {
-        final res =
-            await (_queryIssue(context) as Future<GIssueData_repository>);
+        final res = await _queryIssue(context);
         if (res.issueOrPullRequest!.G__typename == 'Issue') {
           final issue = res.issueOrPullRequest
               as GIssueData_repository_issueOrPullRequest__asIssue;
           return LongListPayload(
             header: res,
             totalCount: issue.timelineItems.totalCount,
-            cursor: issue.timelineItems.pageInfo.endCursor,
+            cursor: issue.timelineItems.pageInfo.endCursor!,
             leadingItems: issue.timelineItems.nodes!.toList(),
             trailingItems: [],
           );
@@ -275,22 +274,21 @@ class GhIssueScreen extends StatelessWidget {
           return LongListPayload(
             header: res,
             totalCount: pr.timelineItems.totalCount,
-            cursor: pr.timelineItems.pageInfo.endCursor,
+            cursor: pr.timelineItems.pageInfo.endCursor!,
             leadingItems: pr.timelineItems.nodes!.toList(),
             trailingItems: [],
           );
         }
       },
       onLoadMore: (_cursor) async {
-        final res = await (_queryIssue(context, cursor: _cursor)
-            as Future<GIssueData_repository>);
+        final res = await _queryIssue(context, cursor: _cursor);
         if (res.issueOrPullRequest!.G__typename == 'Issue') {
           final issue = res.issueOrPullRequest
               as GIssueData_repository_issueOrPullRequest__asIssue;
           return LongListPayload(
             header: res,
             totalCount: issue.timelineItems.totalCount,
-            cursor: issue.timelineItems.pageInfo.endCursor,
+            cursor: issue.timelineItems.pageInfo.endCursor!,
             leadingItems: issue.timelineItems.nodes!.toList(),
           );
         } else {
@@ -299,7 +297,7 @@ class GhIssueScreen extends StatelessWidget {
           return LongListPayload(
             header: res,
             totalCount: pr.timelineItems.totalCount,
-            cursor: pr.timelineItems.pageInfo.endCursor,
+            cursor: pr.timelineItems.pageInfo.endCursor!,
             leadingItems: pr.timelineItems.nodes!.toList(),
           );
         }
diff --git a/lib/screens/gh_repo.dart b/lib/screens/gh_repo.dart
index 768dee1..dea0265 100644
--- a/lib/screens/gh_repo.dart
+++ b/lib/screens/gh_repo.dart
@@ -270,7 +270,7 @@ class GhRepoScreen extends StatelessWidget {
                     leftIconData: Octicons.history,
                     text: Text(AppLocalizations.of(context)!.commits),
                     rightWidget: Text(
-                        ((ref.target as GRepoCommit).history?.totalCount ?? 0)
+                        ((ref.target as GRepoCommit).history.totalCount)
                             .toString()),
                     url: '/github/$owner/$name/commits/${ref.name}',
                   ),
diff --git a/lib/screens/gh_search.dart b/lib/screens/gh_search.dart
index 5346426..bd48733 100644
--- a/lib/screens/gh_search.dart
+++ b/lib/screens/gh_search.dart
@@ -25,7 +25,7 @@ class _GhSearchScreenState extends State<GhSearchScreen> {
 
   TextEditingController? _controller;
 
-  String get _keyword => _controller!.text?.trim() ?? '';
+  String get _keyword => _controller!.text.trim();
 
   @override
   void initState() {
diff --git a/lib/screens/gl_search.dart b/lib/screens/gl_search.dart
index b232344..66e39bc 100644
--- a/lib/screens/gl_search.dart
+++ b/lib/screens/gl_search.dart
@@ -26,7 +26,7 @@ class _GlSearchScreenState extends State<GlSearchScreen> {
 
   TextEditingController? _controller;
 
-  String get _keyword => _controller!.text?.trim() ?? '';
+  String get _keyword => _controller!.text.trim();
 
   @override
   void initState() {