I am getting this error

java.lang.ExceptionInInitializerError
at com.comphenix.protocol.injector.netty.ProtocolInjector.(ProtocolInjector.java:69)
at com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:202)
at com.comphenix.protocol.injector.PacketFilterBuilder.buildInternal(PacketFilterBuilder.java:185)
at com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:177)
at com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:203)
at org.bukkit.craftbukkit.v1_16_R3.CraftServer.loadPlugins(CraftServer.java:399)
at net.minecraft.server.v1_16_R3.DedicatedServer.init(DedicatedServer.java:269)
at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:1074)
at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:291)
at java.base/java.lang.Thread.run(Thread.java:1589)
Caused by: java.lang.UnsupportedOperationException: Cannot define class using reflection: Unable to make protected java.lang.Package java.lang.ClassLoader.getPackage(java.lang.String) accessible: module java.base does not "opens java.lang" to unnamed module @6625de8f
at com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection$Dispatcher$Initializable$Unavailable.defineClass(ClassInjector.java:471)
at com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$UsingReflection.injectRaw(ClassInjector.java:283)
at com.comphenix.net.bytebuddy.dynamic.loading.ClassInjector$AbstractBase.inject(ClassInjector.java:117)
at com.comphenix.net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default$InjectionDispatcher.load(ClassLoadingStrategy.java:243)
at com.comphenix.net.bytebuddy.dynamic.loading.ClassLoadingStrategy$Default.load(ClassLoadingStrategy.java:150)
at com.comphenix.net.bytebuddy.dynamic.TypeResolutionStrategy$Passive.initialize(TypeResolutionStrategy.java:101)
at com.comphenix.net.bytebuddy.dynamic.DynamicType$Default$Unloaded.load(DynamicType.java:6161)
at com.comphenix.protocol.injector.server.TemporaryPlayerFactory.setupProxyPlayerConstructor(TemporaryPlayerFactory.java:187)
at com.comphenix.protocol.injector.server.TemporaryPlayerFactory.(TemporaryPlayerFactory.java:51)
... 10 more
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@40d2ae63[
statistics=
backgroundCompiler=
packetTask=-1
tickCounter=0
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@3e06eb9d
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@6bf2eb88
redirectHandler=
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=org.bukkit.plugin.java.JavaPluginLoader@1bc85eb9
server=CraftServer{serverName=Paper,serverVersion=git-Paper-794,minecraftVersion=1.16.5}
file=plugins/ProtocolLib.jar
description=org.bukkit.plugin.PluginDescriptionFile@862c9b6
dataFolder=plugins/ProtocolLib
classLoader=PluginClassLoader{plugin=ProtocolLib v4.8.0, pluginEnabled=false, url=plugins/ProtocolLib.jar}
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins/ProtocolLib/config.yml
logger=com.destroystokyo.paper.utils.PaperPluginLogger@75af1115
]
Version:
ProtocolLib v4.8.0
Java Version:
19.0.2
Server:
git-Paper-794 (MC: 1.16.5)

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