Paper accepts empty MOTD while vanilla doesn't

[PerchunPak]

Expected behavior

$ docker run --rm -p 25565:25565 -e EULA=TRUE -e MOTD= itzg/minecraft-server
... <snipped> ...
[22:25:48] [Netty Epoll Server IO #6/ERROR]: Error sending packet clientbound/minecraft:disconnect                                                                                                                                    
io.netty.handler.codec.EncoderException: Sending unknown packet 'clientbound/minecraft:disconnect'                                                                                                                                    
        at zd.a(SourceFile:50) ~[server-1.21.5.jar:?]                                                                                                                                                                                 
        at zd.encode(SourceFile:14) ~[server-1.21.5.jar:?]                                                                                                                                                                            
        at wj.a(SourceFile:26) ~[server-1.21.5.jar:?]                                                                                                                                                                                 
        at wj.encode(SourceFile:12) ~[server-1.21.5.jar:?]                                                                                                                                                                            
        at io.netty.handler.codec.MessageToByteEncoder.write(MessageToByteEncoder.java:107) ~[netty-codec-4.1.118.Final.jar:4.1.118.Final]                                                                                            
        at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:893) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeWrite(AbstractChannelHandlerContext.java:875) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:984) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:868) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.ChannelOutboundHandlerAdapter.write(ChannelOutboundHandlerAdapter.java:113) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at vv$2.write(SourceFile:530) ~[server-1.21.5.jar:?]                                                       
        at io.netty.channel.AbstractChannelHandlerContext.invokeWrite0(AbstractChannelHandlerContext.java:893) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeWriteAndFlush(AbstractChannelHandlerContext.java:956) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.write(AbstractChannelHandlerContext.java:982) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:950) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.writeAndFlush(AbstractChannelHandlerContext.java:1000) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.DefaultChannelPipeline.writeAndFlush(DefaultChannelPipeline.java:974) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannel.writeAndFlush(AbstractChannel.java:305) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at vv.c(SourceFile:350) ~[server-1.21.5.jar:?]
        at vv.b(SourceFile:343) ~[server-1.21.5.jar:?]
        at vv.a(SourceFile:325) ~[server-1.21.5.jar:?]
        at vv.a(SourceFile:319) ~[server-1.21.5.jar:?]
        at vv.exceptionCaught(SourceFile:170) ~[server-1.21.5.jar:?]                                               
        at io.netty.channel.AbstractChannelHandlerContext.invokeExceptionCaught(AbstractChannelHandlerContext.java:346) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeExceptionCaught(AbstractChannelHandlerContext.java:325) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireExceptionCaught(AbstractChannelHandlerContext.java:317) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.ChannelInboundHandlerAdapter.exceptionCaught(ChannelInboundHandlerAdapter.java:143) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeExceptionCaught(AbstractChannelHandlerContext.java:346) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:447) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.flow.FlowControlHandler.dequeue(FlowControlHandler.java:202) ~[netty-handler-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.flow.FlowControlHandler.channelRead(FlowControlHandler.java:164) ~[netty-handler-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:346) ~[netty-codec-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:333) ~[netty-codec-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:455) ~[netty-codec-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:290) ~[netty-codec-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:289) ~[netty-handler-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1357) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:868) ~[netty-transport-4.1.118.Final.jar:4.1.118.Final]
        at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:799) ~[netty-transport-classes-epoll-4.1.118.Final.jar:4.1.118.Final]                                     
        at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:501) ~[netty-transport-classes-epoll-4.1.118.Final.jar:4.1.118.Final]                                                                               
        at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:399) ~[netty-transport-classes-epoll-4.1.118.Final.jar:4.1.118.Final]                                                                                        
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:998) ~[netty-common-4.1.118.Final.jar:4.1.118.Final]                                                                               
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.118.Final.jar:4.1.118.Final]                                                                                                  
        at java.base/java.lang.Thread.run(Unknown Source) [?:?]

Observed/Actual behavior

Server starts just fine, but its response doesn't include description, which leads to py-mine/mcstatus#992

Steps/models to reproduce

Just put motd= in server.properties

$ docker run --rm -it -p 25565:25565 -e EULA=TRUE -e TYPE=PAPER -e MOTD="" itzg/minecraft-server

Plugin and Datapack List

None

Paper version

> version
[07:09:56 INFO]: Checking version, please wait...
[07:09:56 INFO]: This server is running Paper version 1.21.4-227-ver/1.21.4@7675321 (2025-04-28T19:07:04Z) (Implementing API version 1.21.4-R0.1-SNAPSHOT)
You are running the latest version

Other

No response

[Warriorrrr]

The description field missing seems fine to me, it's an optional field so it's possible for the server to not include it (see https://minecraft.wiki/w/Java_Edition_protocol/Server_List_Ping#Status_Response).

The solution in the pr linked to the mentioned issue is the correct one, nothing on paper's side really needs to change.

[PerchunPak]

Those docs are created from reverse engineering, but I guess you know more than me so you are right