12:27:19 PM [INFO] > Stack Trace:
12:27:19 PM [INFO] > java.lang.IllegalArgumentException: Unable to find a field that matches {modifiers=[required: 10000, banned: 1000], type={ type input instanceof interface java.util.Map }}
12:27:19 PM [INFO] > at com.comphenix.protocol.reflect.FuzzyReflection.getField(FuzzyReflection.java:352)
12:27:19 PM [INFO] > at com.comphenix.protocol.injector.packet.PacketRegistry.createNewRegister(PacketRegistry.java:183)
12:27:19 PM [INFO] > at com.comphenix.protocol.injector.packet.PacketRegistry.initialize(PacketRegistry.java:334)
12:27:19 PM [INFO] > at com.comphenix.protocol.injector.packet.PacketRegistry.getClientPacketTypes(PacketRegistry.java:369)
12:27:19 PM [INFO] > at com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:120)
12:27:19 PM [INFO] > at com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:121)
12:27:19 PM [INFO] > at com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:183)
12:27:19 PM [INFO] > at org.bukkit.craftbukkit.v1_21_R1.CraftServer.loadPlugins(CraftServer.java:461)
12:27:19 PM [INFO] > at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:236)
12:27:19 PM [INFO] > at net.minecraft.server.MinecraftServer.y(MinecraftServer.java:1017)
12:27:19 PM [INFO] > at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:318)
12:27:19 PM [INFO] > at java.base/java.lang.Thread.run(Thread.java:1583)
12:27:19 PM [INFO] > Dump:
12:27:19 PM [INFO] > Parameters:
12:27:19 PM [INFO] > [NULL]
12:27:19 PM [INFO] > Sender:
12:27:19 PM [INFO] > com.comphenix.protocol.ProtocolLib@1dd4c94d[
12:27:19 PM [INFO] > statistics=
12:27:19 PM [INFO] > packetTask=
12:27:19 PM [INFO] > tickCounter=0
12:27:19 PM [INFO] > configExpectedMod=-1
12:27:19 PM [INFO] > updater=com.comphenix.protocol.updater.SpigotUpdater@2c057299
12:27:19 PM [INFO] > redirectHandler=
12:27:19 PM [INFO] > scheduler=com.comphenix.protocol.scheduler.DefaultScheduler@17a048f5
12:27:19 PM [INFO] > commandProtocol=
12:27:19 PM [INFO] > commandPacket=
12:27:19 PM [INFO] > commandFilter=
12:27:19 PM [INFO] > packetLogging=
12:27:19 PM [INFO] > skipDisable=false
12:27:19 PM [INFO] > isEnabled=false
12:27:19 PM [INFO] > loader=org.bukkit.plugin.java.JavaPluginLoader@318bfc89
12:27:19 PM [INFO] > server=CraftServer{serverName=CraftBukkit,serverVersion=4226-Spigot-146439e-2889b3a,minecraftVersion=1.21}
12:27:19 PM [INFO] > file=plugins\ProtocolLib.jar
12:27:19 PM [INFO] > description=org.bukkit.plugin.PluginDescriptionFile@7b5a522
12:27:19 PM [INFO] > classLoader=org.bukkit.plugin.java.PluginClassLoader@2158c7a1
12:27:19 PM [INFO] > dataFolder=plugins\ProtocolLib
12:27:19 PM [INFO] > naggable=true
12:27:19 PM [INFO] > newConfig=YamlConfiguration[path='', root='YamlConfiguration']
12:27:19 PM [INFO] > configFile=plugins\ProtocolLib\config.yml
12:27:19 PM [INFO] > logger=org.bukkit.plugin.PluginLogger@4fb26f22
12:27:19 PM [INFO] > ]
12:27:19 PM [INFO] > Version:
12:27:19 PM [INFO] > ProtocolLib v5.2.0-SNAPSHOT-679
12:27:19 PM [INFO] > Java Version:
12:27:19 PM [INFO] > 21.0.3
12:27:19 PM [INFO] > Server:
12:27:19 PM [INFO] > 4226-Spigot-146439e-2889b3a (MC: 1.21)

Resolved in #3207

Should be fixed in the latest dev build so please use the latest dev build and try again: https://ci.dmulloy2.net/job/ProtocolLib/lastSuccessfulBuild/