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]);