Issue with REFER Call

[Vinayak006]

Describe the bug I am experiencing an issue when making a REFER call using the Dart SIP UA library. The call is terminated unexpectedly, and I am receiving the following error messages in the logs:

flutter: [2023-12-27 13:31:43.205] Level.debug refer_subscriber.dart:120 ::: REFER failed
flutter: [2023-12-27 13:31:43.206] Level.debug refer_subscriber.dart:122 ::: emit "requestFailed"
flutter: [2023-12-27 13:31:43.206] Level.error event_manager.dart:111 ::: type 'String' is not a subtype of type 'ErrorCause?'
flutter: #0      ReferSubscriber._requestFailed (package:sip_ua/src/rtc_session/refer_subscriber.dart:124:61)
#1      ReferSubscriber.sendRefer.<anonymous closure> (package:sip_ua/src/rtc_session/refer_subscriber.dart:64:7)
#2      EventManager.emit (package:sip_ua/src/event_manager/event_manager.dart:109:17)
#3      DialogRequestSender.send.<anonymous closure> (package:sip_ua/src/dialog/request_sender.dart:38:22)
#4      EventManager.emit (package:sip_ua/src/event_manager/event_manager.dart:109:17)
#5      RequestSender.send.<anonymous closure> (package:sip_ua/src/request_sender.dart:48:22)
#6      EventManager.emit (package:sip_ua/src/event_manager/event_manager.dart:109:17)
#7      NonInviteClientTransaction.timer_F (package:sip_ua/src/transactions/non_invite_client.dart:65:20)
#8      NonInviteClientTransaction.send.<anonymous closure> (package:sip_ua/src/transactions/non_invite_client.dart:43:7)
#9      Timer._createTimer.<anonymous closure> (dart:async-patch/timer_patch.dart:18:15)
#10     _Timer._runTimers (dart:isolate-patch/timer_impl.dart:398:19)
#11     _Timer._handleMessage (dart:isolate-patch/timer_impl.dart:429:5)
#12     _RawReceivePort._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

To Reproduce Steps to reproduce the behaviour: I have made 'call.refer(target)' and with the above logs call ended and the refer also failed

Expected behaviour I have expected that in 'onCallStateChanged', would have received a CallState.REFER. But I don't receive any change in callstate when making refer().

System Infomation() Flutter SDK Version: 3.16.3 sip_ua: 0.5.8