fix(llc): when removing current user from channel check for null in the callback

Closes #1753

packages/stream_chat/CHANGELOG.md

@@ -6,6 +6,8 @@
   update message with `type: reply`.
 - [[#1724]](https://github.com/GetStream/stream-chat-flutter/issues/1724) Fixed sendFile error
   on `AttachmentFile` with `bytes` and no `name`.
+- [[#1753]](https://github.com/GetStream/stream-chat-flutter/issues/1753) Fixed Unhandled null 
+  check operator exception when user is removed from a channel.
 
 ## 6.8.0
 

packages/stream_chat/lib/src/client/client.dart

@@ -1658,7 +1658,7 @@ class ClientState {
       )
           .listen((event) async {
         final isCurrentUser = event.user!.id == currentUser!.id;
-        if (isCurrentUser) {
+        if (isCurrentUser && event.channel != null) {
           final eventChannel = event.channel!;
           await _client.chatPersistenceClient
               ?.deleteChannels([eventChannel.cid]);

packages/stream_chat_flutter/example/lib/debug/actions/add_user.dart

@@ -0,0 +1,47 @@
+// ignore_for_file: public_member_api_docs
+
+import 'package:flutter/material.dart';
+import 'package:stream_chat_flutter/stream_chat_flutter.dart';
+
+import 'package:stream_chat_flutter_example/debug/error_dialog.dart';
+
+class DebugAddUser extends StatelessWidget {
+  const DebugAddUser({
+    super.key,
+    required this.client,
+    required this.channel,
+  });
+
+  final StreamChatClient client;
+  final Channel channel;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.all(8),
+      child: TextField(
+        decoration: const InputDecoration(
+          labelText: 'Add User',
+          hintText: 'User Id',
+          isDense: true,
+          border: OutlineInputBorder(),
+        ),
+        onSubmitted: (value) async {
+          final userId = value.trim();
+          try {
+            debugPrint('[addUser] userId: $userId');
+            final result = await client.addChannelMembers(
+              channel.id!,
+              channel.type,
+              [userId],
+            );
+            debugPrint('[addUser] result: $result');
+          } catch (e) {
+            debugPrint('[addUser] failed: $e');
+            showErrorDialog(context, e, 'Add User');
+          }
+        },
+      ),
+    );
+  }
+}

packages/stream_chat_flutter/example/lib/debug/actions/remove_user.dart

@@ -0,0 +1,47 @@
+// ignore_for_file: public_member_api_docs
+
+import 'package:flutter/material.dart';
+import 'package:stream_chat_flutter/stream_chat_flutter.dart';
+
+import 'package:stream_chat_flutter_example/debug/error_dialog.dart';
+
+class DebugRemoveUser extends StatelessWidget {
+  const DebugRemoveUser({
+    super.key,
+    required this.client,
+    required this.channel,
+  });
+
+  final StreamChatClient client;
+  final Channel channel;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+      padding: const EdgeInsets.all(8),
+      child: TextField(
+        decoration: const InputDecoration(
+          labelText: 'Remove User',
+          hintText: 'User Id',
+          isDense: true,
+          border: OutlineInputBorder(),
+        ),
+        onSubmitted: (value) async {
+          final userId = value.trim();
+          try {
+            debugPrint('[removeUser] userId: $userId');
+            final result = await client.removeChannelMembers(
+              channel.id!,
+              channel.type,
+              [userId],
+            );
+            debugPrint('[removeUser] result: $result');
+          } catch (e) {
+            debugPrint('[removeUser] failed: $e');
+            showErrorDialog(context, e, 'Remove User');
+          }
+        },
+      ),
+    );
+  }
+}

packages/stream_chat_flutter/example/lib/debug/channel_page.dart

@@ -4,9 +4,11 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:stream_chat_flutter/stream_chat_flutter.dart';
+import 'package:stream_chat_flutter_example/debug/actions/add_user.dart';
 import 'package:stream_chat_flutter_example/debug/actions/ban_user.dart';
 import 'package:stream_chat_flutter_example/debug/actions/mute_user.dart';
 import 'package:stream_chat_flutter_example/debug/actions/remove_shadow_ban.dart';
+import 'package:stream_chat_flutter_example/debug/actions/remove_user.dart';
 import 'package:stream_chat_flutter_example/debug/actions/shadow_ban.dart';
 import 'package:stream_chat_flutter_example/debug/actions/unban_user.dart';
 import 'package:stream_chat_flutter_example/debug/actions/unmute_user.dart';
@@ -82,6 +84,10 @@ class _DebugChannelPageState extends State<DebugChannelPage> {
             DebugShadowBan(client: _channel.client),
             const SizedBox(height: 8),
             DebugRemoveShadowBan(client: _channel.client),
+            const SizedBox(height: 8),
+            DebugAddUser(client: _channel.client, channel: _channel),
+            const SizedBox(height: 8),
+            DebugRemoveUser(client: _channel.client, channel: _channel),
           ],
         ),
       ),