Version Info
4.6.0

Additional context
when I join my server this pops up in the console (I am the only person on the server).

[22:51:09 ERROR]: [ProtocolLib] INTERNAL ERROR: Cannot compile structure. Disabing compiler.
If this problem hasn't already been reported, please open a ticket
at https://github.com/dmulloy2/ProtocolLib/issues with the following data:
Stack Trace:
java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @1ec83133
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:199)
at java.base/java.lang.reflect.Method.setAccessible(Method.java:193)
at com.comphenix.protocol.reflect.compiler.StructureCompiler.generateClass(StructureCompiler.java:299)
at com.comphenix.protocol.reflect.compiler.StructureCompiler.compile(StructureCompiler.java:213)
at com.comphenix.protocol.reflect.compiler.BackgroundCompiler$2.call(BackgroundCompiler.java:204)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
at java.base/java.lang.Thread.run(Thread.java:831)
Dump:
Parameters:
com.comphenix.protocol.reflect.StructureModifier@14d08b30[
targetType=class net.minecraft.server.v1_16_R3.NBTTagCompound
target=
converter=
fieldType=interface java.util.Map
data=[public final java.util.Map net.minecraft.server.v1_16_R3.NBTTagCompound.map]
defaultFields={}
subtypeCache={}
customConvertHandling=false
useStructureCompiler=true
]
manager:
com.comphenix.protocol.injector.PacketFilterManager@4a1e0506[
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@4bcb25c9
packetListeners=[PacketAdapter[plugin=MyPet, sending=EMPTY_WHITELIST, receiving=ListeningWhitelist[priority=NORMAL, packets=[USE_ENTITY[class=PacketPlayInUseEntity, id=14]], gamephase=PLAYING, options=[]]], PacketAdapter[plugin=IllegalStack, sending=EMPTY_WHITELIST, receiving=ListeningWhitelist[priority=NORMAL, packets=[USE_ENTITY[class=PacketPlayInUseEntity, id=14]], gamephase=PLAYING, options=[]]], PacketAdapter[plugin=SuperVanish, sending=ListeningWhitelist[priority=LOW, packets=[ENTITY_METADATA[class=PacketPlayOutEntityMetadata, id=68], PLAYER_INFO[class=PacketPlayOutPlayerInfo, id=50], ABILITIES[class=PacketPlayOutAbilities, id=48]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=SuperVanish, sending=ListeningWhitelist[priority=NORMAL, packets=[PLAYER_INFO[class=PacketPlayOutPlayerInfo, id=50]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=MyCommand, sending=EMPTY_WHITELIST, receiving=ListeningWhitelist[priority=NORMAL, packets=[UPDATE_SIGN[class=PacketPlayInUpdateSign, id=43]], gamephase=PLAYING, options=[]]], PacketAdapter[plugin=HolographicDisplays, sending=ListeningWhitelist[priority=NORMAL, packets=[ENTITY_METADATA[class=PacketPlayOutEntityMetadata, id=68], SPAWN_ENTITY_LIVING[class=PacketPlayOutSpawnEntityLiving, id=2], SPAWN_ENTITY[class=PacketPlayOutSpawnEntity, id=0], REL_ENTITY_MOVE_LOOK[class=PacketPlayOutRelEntityMoveLook, id=40], REL_ENTITY_MOVE[class=PacketPlayOutRelEntityMove, id=39]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=Orebfuscator, sending=ListeningWhitelist[priority=NORMAL, packets=[UNLOAD_CHUNK[class=PacketPlayOutUnloadChunk, id=28]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], com.comphenix.protocol.async.NullPacketListener@37bc92ce, PacketAdapter[plugin=PlayerWarps, sending=EMPTY_WHITELIST, receiving=ListeningWhitelist[priority=NORMAL, packets=[UPDATE_SIGN[class=PacketPlayInUpdateSign, id=43]], gamephase=PLAYING, options=[]]], PacketAdapter[plugin=SuperVanish, sending=ListeningWhitelist[priority=HIGH, packets=[PLAYER_INFO[class=PacketPlayOutPlayerInfo, id=50]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=SuperVanish, sending=ListeningWhitelist[priority=NORMAL, packets=[OUT_SERVER_INFO[class=PacketStatusOutServerInfo, id=0]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST], PacketAdapter[plugin=MyPet, sending=ListeningWhitelist[priority=NORMAL, packets=[ENTITY_HEAD_ROTATION[class=PacketPlayOutEntityHeadRotation, id=58], ENTITY_LOOK[class=PacketPlayOutEntityLook, id=41], REL_ENTITY_MOVE_LOOK[class=PacketPlayOutRelEntityMoveLook, id=40], ENTITY_TELEPORT[class=PacketPlayOutEntityTeleport, id=86]], gamephase=PLAYING, options=[]], receiving=EMPTY_WHITELIST]]
packetInjector=com.comphenix.protocol.injector.netty.ProtocolInjector$5@dfd5bce
playerInjection=com.comphenix.protocol.injector.netty.ProtocolInjector$4@1de4d84a
inputBufferedPackets=[]
recievedListeners=com.comphenix.protocol.injector.SortedPacketListenerList@27e8c8c5
sendingListeners=com.comphenix.protocol.injector.SortedPacketListenerList@359f549c
hasClosed=false
classLoader=PluginClassLoader{plugin=ProtocolLib v4.6.0, pluginEnabled=true, url=plugins\ProtocolLib.jar}
reporter=com.comphenix.protocol.ProtocolLib$1@525b5aca
server=CraftServer{serverName=Paper,serverVersion=git-Paper-777,minecraftVersion=1.16.5}
library=ProtocolLib v4.6.0
asyncFilterManager=com.comphenix.protocol.async.AsyncFilterManager@889ad5e
knowsServerPackets=true
knowsClientPackets=true
phaseLoginCount=1
phasePlayingCount=12
packetCreation=false
nettyInjector=com.comphenix.protocol.injector.netty.ProtocolInjector@54344b23
pluginVerifier=com.comphenix.protocol.injector.PluginVerifier@7a7cbcc9
hasRecycleDistance=true
minecraftVersion=(MC: 1.16.5)
debug=false
]
Sender:
com.comphenix.protocol.reflect.compiler.BackgroundCompiler@70ec5532[
listeners={com.comphenix.protocol.reflect.compiler.StructureCompiler$StructureKey@16fb174e=[com.comphenix.protocol.reflect.compiler.BackgroundCompiler$1@76c006ca], com.comphenix.protocol.reflect.compiler.StructureCompiler$StructureKey@cf8b2a01=[com.comphenix.protocol.reflect.compiler.BackgroundCompiler$1@db3662, com.comphenix.protocol.reflect.compiler.BackgroundCompiler$1@1fde5844, com.comphenix.protocol.reflect.compiler.BackgroundCompiler$1@d09cb48, com.comphenix.protocol.reflect.compiler.BackgroundCompiler$1@7b896a75]}
listenerLock=java.lang.Object@22382b40
compiler=com.comphenix.protocol.reflect.compiler.StructureCompiler@4f495b3b
enabled=false
shuttingDown=false
executor=java.util.concurrent.Executors$FinalizableDelegatedExecutorService@c599a11
reporter=com.comphenix.protocol.ProtocolLib$1@525b5aca
unknownPermGenBean=java.lang.Object@3cb3932d
permGenBean=
disablePermGenFraction=0.65
]
Version:
ProtocolLib v4.6.0
Java Version:
16.0.1
Server:
git-Paper-777 (MC: 1.16.5)

This is fixed in the latest dev builds. Find them here: https://ci.dmulloy2.net/job/ProtocolLib/