fix Message Packet serialization

mirai-api-http/src/main/kotlin/net/mamoe/mirai/api/http/dto/DTO.kt

@@ -2,17 +2,17 @@ package net.mamoe.mirai.api.http.dto
 
 import kotlinx.serialization.*
 import kotlinx.serialization.json.Json
-import kotlinx.serialization.modules.SerializersModule
 
 interface DTO
 
 object MiraiJson {
-    val json = Json(context = SerializersModule {
-        polymorphic(MessagePacketDTO.serializer()) {
-            GroupMessagePacketDTO::class with GroupMessagePacketDTO.serializer()
-            FriendMessagePacketDTO::class with FriendMessagePacketDTO.serializer()
-        }
-    })
+//    val json = Json(context = SerializersModule {
+//        polymorphic(MessagePacketDTO.serializer()) {
+//            GroupMessagePacketDTO::class with GroupMessagePacketDTO.serializer()
+//            FriendMessagePacketDTO::class with FriendMessagePacketDTO.serializer()
+//        }
+//    })
+    val json = Json
 }
 
 // 解析失败时直接返回null，由路由判断响应400状态

mirai-api-http/src/main/kotlin/net/mamoe/mirai/api/http/dto/MessageDTO.kt

@@ -21,6 +21,10 @@ data class FriendMessagePacketDTO(val sender: QQDTO) : MessagePacketDTO()
 @SerialName("GroupMessage")
 data class GroupMessagePacketDTO(val sender: MemberDTO) : MessagePacketDTO()
 
+@Serializable
+@SerialName("UnKnownMessage")
+data class UnKnownMessagePacketDTO(val msg: String) : MessagePacketDTO()
+
 // Message
 @Serializable
 @SerialName("At")
@@ -58,11 +62,11 @@ sealed class MessageDTO : DTO
 /*
     Extend function
  */
-suspend fun MessagePacket<*, *>.toDTO(): MessagePacketDTO? = when (this) {
+suspend fun MessagePacket<*, *>.toDTO(): MessagePacketDTO = when (this) {
     is FriendMessage -> FriendMessagePacketDTO(QQDTO(sender))
     is GroupMessage -> GroupMessagePacketDTO(MemberDTO(sender, senderName))
-    else -> null
-}?.apply { messageChain = Array(message.size){ message[it].toDTO() }}
+    else -> UnKnownMessagePacketDTO("UnKnown Message Packet")
+}.apply { messageChain = Array(message.size){ message[it].toDTO() }}
 
 fun MessageChainDTO.toMessageChain() =
     MessageChain().apply { this@toMessageChain.forEach { add(it.toMessage()) } }