[BUG] 10002 exception occurs when `offlinePushInfo` is `null`

[cipchk]

OpenIM Server Version

3.8.2

Operating System and CPU Architecture

Linux (AMD)

Deployment Method

Docker Deployment

Bug Description and Steps to Reproduce

当调用 sendMessage 并不传递 offlinePushInfo 值（或给 null）时，产生以下异常。

flutter: │ 🐛 ChatView,11:50:33.651:message send failed e :PlatformException(10002, unexpected end of JSON input, null, null)  #0      StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:646:7)
flutter: │ 🐛 #1      MethodChannel._invokeMethod (package:flutter/src/services/platform_channel.dart:334:18)
flutter: │ 🐛 <asynchronous suspension>
flutter: │ 🐛 #2      MessageManager.sendMessage.<anonymous closure> (package:flutter_openim_sdk/src/manager/im_message_manager.dart:53:17)
flutter: │ 🐛 <asynchronous suspension>
flutter: │ 🐛 #3      ChatLogic._sendMessage.<anonymous closure> (package:im/pages/chat/logic.dart:674:15)
flutter: │ 🐛 <asynchronous suspension>
flutter: │ 🐛 #4      ChatLogic._sendMessage.<anonymous closure> (package:im/pages/chat/logic.dart:679:20)
flutter: │ 🐛 <asynchronous suspension>

Screenshots Link

No response

[cipchk]

另外一点所有 SDK 里面的 offlinePushInfo 发送消息接口都是必填，那么应该怎么处理群不推送离线消息呢？

[OpenIM-Robot]

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Another point is that the offlinePushInfo message sending interface in all SDKs is required. So how should we deal with the group not pushing offline messages?