jpush
删除消息，撤回消息接口调完之后，再去调用获取历史消息，仍然可以获取到
这两个接口： jmessage.retractMessage(target: type, serverMessageId: messageId); jmessage.deleteMessageById(type: type, messageId: messageId);
调用完，再调用获取历史消息接口： jmessage.getHistoryMessages(type: type, from: from, limit: limit, isDescend: false); 仍然能获取到被删除或被撤回的消息
我这边是撤回消息后 再调用jmessage.getHistoryMessages会因为又Null，导致整个历史消息获取失败。极光这都不咋更新 感觉废了
E/flutter (13435): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: type 'Null' is not a subtype of type 'String' E/flutter (13435): #0 JMNormalMessage.generateMessageFromJson (package:jmessage_flutter/jmessage_flutter.dart:2041:70) E/flutter (13435): #1 JmessageFlutter.getHistoryMessages (package:jmessage_flutter/jmessage_flutter.dart:893:35)
