NetworkException: null
java.lang.NullPointerException: type cannot be null
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:921) ~[guava-32.1.2-jre.jar:?]
at com.comphenix.protocol.injector.StructureCache.getStructure(StructureCache.java:138) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.events.PacketContainer.(PacketContainer.java:126) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.injector.netty.manager.NetworkManagerInjector.onPacketSending(NetworkManagerInjector.java:96) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.injector.netty.channel.NettyChannelInjector.processOutbound(NettyChannelInjector.java:553) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.injector.netty.channel.NettyChannelProxy.processPacketOutbound(NettyChannelProxy.java:266) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.injector.netty.channel.NettyChannelProxy.writeAndFlush(NettyChannelProxy.java:223) ~[ProtocolLib-679.jar:?]
at com.comphenix.protocol.injector.netty.channel.NettyChannelProxy.writeAndFlush(NettyChannelProxy.java:233) ~[ProtocolLib-679.jar:?]

You probably use ProtocolLib 5.1.0 for Minecraft 1.20.2 or late. That's incompatible!
Use this version of ProtocolLib instead: https://ci.dmulloy2.net/job/ProtocolLib//lastBuild/artifact/build/libs/ProtocolLib.jar