It ran perfectly fine up until I tried to join the server. Then it started posting this error over and over again in the logs:

[22:53:14] [Netty Epoll Server IO #0/FATAL]: java.lang.NoClassDefFoundError: Could not initialize class net.minecraft.network.ConnectionProtocol
[22:53:14] [Netty Epoll Server IO #0/WARN]: An exception 'java.lang.NoClassDefFoundError: Could not initialize class net.minecraft.network.ConnectionProtocol' [enable DEBUG level for full stacktrace] was thrown by a user handler's exceptionCaught() method while handling the following exception:
io.netty.handler.codec.DecoderException: java.lang.NullPointerException: Cannot invoke "net.minecraft.network.ConnectionProtocol.m_178321_(net.minecraft.network.protocol.PacketFlow, int, net.minecraft.network.FriendlyByteBuf)" because the return value of "io.netty.util.Attribute.get()" is null
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:477) ~[netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:276) ~[netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:311) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:432) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:276) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at net.minecraft.server.network.LegacyQueryHandler.channelRead(LegacyQueryHandler.java:94) [server-1.18.1-20211210.034407-srg.jar%23292!/:?]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.timeout.IdleStateHandler.channelRead(IdleStateHandler.java:286) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.epollInReady(AbstractEpollStreamChannel.java:795) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.epoll.EpollEventLoop.processReady(EpollEventLoop.java:480) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:378) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:986) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) [netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at java.lang.Thread.run(Thread.java:833) [?:?]
Caused by: java.lang.NullPointerException: Cannot invoke "net.minecraft.network.ConnectionProtocol.m_178321_(net.minecraft.network.protocol.PacketFlow, int, net.minecraft.network.FriendlyByteBuf)" because the return value of "io.netty.util.Attribute.get()" is null
at net.minecraft.network.PacketDecoder.decode(PacketDecoder.java:36) ~[server-1.18.1-20211210.034407-srg.jar%23292!/:?]
at io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:507) ~[netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:446) ~[netty-all-4.1.68.Final.jar%2332!/:4.1.68.Final]
... 29 more

Holy shit

1.18?

yeah 1.18.1

fixed