readStream method Null safety
- {String? channelUrl}
Returns a stream to listen read event with given channelUrl
It will be triggered every read event if channelUrl is not provided
Implementation
Stream<GroupChannel> readStream({String? channelUrl}) async* {
  if (currentUser == null) throw ConnectionRequiredError();
  await for (final res in _int.streamManager.read.stream) {
    if (channelUrl != null) {
      if (res.channelUrl == channelUrl) yield res;
    } else {
      yield res;
    }
  }
}