type 'String' is not a subtype of type 'int' of 'index'

[ChiJohn]

The following _TypeError was thrown:
type 'String' is not a subtype of type 'int' of 'index'

When the exception was thrown, this was the stack:
#0 Socket.onpacket (package:socket_io_client/src/socket.dart:398:53)
#1 EventEmitter._emit. (package:socket_io_common/src/util/event_emitter.dart:44:14)
#2 List.forEach (dart:core-patch/growable_array.dart:416:8)
#3 EventEmitter._emit (package:socket_io_common/src/util/event_emitter.dart:43:11)
#4 EventEmitter.emitReserved (package:socket_io_common/src/util/event_emitter.dart:57:47)
#5 Manager.ondecoded. (package:socket_io_client/src/manager.dart:276:7)
(elided 11 frames from dart:async)

[ChiJohn]

pubspec.yaml
socket_io_client: ^3.0.0-beta.1

flutter doctor

[jumperchen]

any reproducible example? or please test with the latest 3.0.0-beta.4 version to give it a try.