Flutter Android JMessage downloadThumbImage 报错

机型：Redmi 5
版本：Android 8.1.0 (API 27)
问题描述：Android下载缩略图时报错，IOS版本同样的代码是正常的。文档里参数target描述的不是很清楚，看java代码应该是有type和username就可以了，试了几种target，android都是报同样的错误，ios可以正常获取到图片。另外downloadVoiceFile也有同样的错误。
代码： final JMSingle kMockUser = JMSingle.fromJson({
'username': 'gaohong',
'appKey': '285e5d42757ef682045537c4',
});
Map resJson = await _jmessage.downloadThumbImage(
target: target,
messageId: messageId,
);
日志：E/flutter ( 4471): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: PlatformException(3, No such message, )
E/flutter ( 4471): #0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:564:7)
E/flutter ( 4471): #1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:316:33)
E/flutter ( 4471):
E/flutter ( 4471): #2 JmessageFlutter.downloadThumbImage (package:jmessage_flutter/jmessage_flutter.dart:1066:34)