LevelledMobs error after upgrading from Paper 1.21.5 #69 to #73 (Cannot invoke "java.lang.reflect.Constructor.newInstance(Object[])")

[ExtRIELICi]

Expected behavior

LevelledMobs plugin should load just fine, as it did before I upgraded from version # 69 to # 73. The plugin didn’t receive any updates, and nothing changed except for the replacement of the Paper .jar file.

Observed/Actual behavior

LevelledMobs shows an error, right after upgrading to a newer Paper build.

Steps/models to reproduce

1. Update to Paper 1.21.5 # 73 (the latest version as of the time writing this).
2. Restart the server with LevelledMobs plugin installed
3. LevelledMobs outputs an error.

Plugin and Datapack List

LevelledMobs, ViaVersion, ViaBackwards, SeeMore.

Paper version

This server is running Paper version 1.21.5-73-main@ab0253f (2025-05-07T00:19:05Z) (Implementing API version 1.21.5-R0.1-SNAPSHOT)

Other

[20:56:05 ERROR]: [LevelledMobs] Error initializing plugin 'LevelledMobs-4.3.1 b112.jar' in folder 'plugins/.paper-remapped' (Is it up to date?)
java.lang.NullPointerException: Cannot invoke "java.lang.reflect.Constructor.newInstance(Object[])" because "io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.pluginCommandNodeConstructor" is null
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.asPluginCommand(PaperCommandRegistration.java:168) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.registerCommandNode(PaperCommandRegistration.java:121) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPIBukkit.registerCommandNode(CommandAPIBukkit.java:462) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPIHandler.register(CommandAPIHandler.java:618) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.AbstractCommandAPICommand.register(AbstractCommandAPICommand.java:307) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPICommand.register(CommandAPICommand.java:60) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.ExecutableCommand.register(ExecutableCommand.java:236) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.commands.CommandHandler.registerCommands(CommandHandler.kt:83) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.commands.CommandHandler.load(CommandHandler.kt:28) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.LevelledMobs.onLoad(LevelledMobs.kt:106) ~[LevelledMobs-4.3.1 b112.jar:?]
        at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:59) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:18) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.storage.SimpleProviderStorage.enter(SimpleProviderStorage.java:39) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.entrypoint.LaunchEntryPointHandler.enter(LaunchEntryPointHandler.java:39) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:567) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:235) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1161) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:308) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]

[ExtRIELICi]

Here is the full console log, in case it's useful:

container@pterodactyl~ java -Xms3072M -Xmx6144M -jar server.jar
Starting org.bukkit.craftbukkit.Main
[20:55:59 INFO]: [bootstrap] Running Java 21 (OpenJDK 64-Bit Server VM 21.0.7+6-LTS; Eclipse Adoptium Temurin-21.0.7+6) on Linux 6.1.0-13-amd64 (amd64)
[20:55:59 INFO]: [bootstrap] Loading Paper 1.21.5-73-main@ab0253f (2025-05-07T00:19:05Z) for Minecraft 1.21.5
[20:55:59 INFO]: [PluginInitializerManager] Initializing plugins...
[20:55:59 INFO]: [PluginInitializerManager] Initialized 4 plugins
[20:55:59 INFO]: [PluginInitializerManager] Bukkit plugins (4):
 - LevelledMobs (4.3.1 b112), SeeMore (1.0.2), ViaBackwards (5.3.2), ViaVersion (5.3.2)
[20:56:02 INFO]: Environment: Environment[sessionHost=https://sessionserver.mojang.com, servicesHost=https://api.minecraftservices.com, name=PROD]
[20:56:02 INFO]: Found non-pack entry './world/datapacks/.DS_Store', ignoring
[20:56:03 INFO]: Loaded 1373 recipes
[20:56:03 INFO]: Loaded 1484 advancements
[20:56:03 INFO]: Starting minecraft server version 1.21.5
[20:56:03 INFO]: Loading properties
[20:56:03 INFO]: This server is running Paper version 1.21.5-73-main@ab0253f (2025-05-07T00:19:05Z) (Implementing API version 1.21.5-R0.1-SNAPSHOT)
[20:56:03 INFO]: [spark] This server bundles the spark profiler. For more information please visit https://docs.papermc.io/paper/profiling
[20:56:03 INFO]: Server Ping Player Sample Count: 0
[20:56:03 INFO]: Using 4 threads for Netty based IO
[20:56:04 INFO]: [MoonriseCommon] Paper is using 1 worker threads, 1 I/O threads
[20:56:04 INFO]: [ChunkTaskScheduler] Chunk system is using population gen parallelism: true
[20:56:04 INFO]: Default game type: SURVIVAL
[20:56:04 INFO]: Generating keypair
[20:56:04 INFO]: Starting Minecraft server on 0.0.0.0:25579
[20:56:04 INFO]: Using epoll channel type
[20:56:04 INFO]: Paper: Using libdeflate (Linux x86_64) compression from Velocity.
[20:56:04 INFO]: Paper: Using OpenSSL 3.x.x (Linux x86_64) cipher from Velocity.
[20:56:04 INFO]: [ViaVersion] Loading server plugin ViaVersion v5.3.2
[20:56:05 INFO]: [ViaVersion] ViaVersion 5.3.2 is now loaded. Registering protocol transformers and injecting...
[20:56:05 INFO]: [ViaVersion] Loading block connection mappings ...
[20:56:05 INFO]: [ViaVersion] Using FastUtil Long2ObjectOpenHashMap for block connections
[20:56:05 INFO]: [ViaBackwards] Loading translations...
[20:56:05 INFO]: [ViaBackwards] Registering protocols...
[20:56:05 INFO]: [SeeMore] Loading server plugin SeeMore v1.0.2
[20:56:05 INFO]: [LevelledMobs] Loading server plugin LevelledMobs v4.3.1 b112
[20:56:05 INFO]: [LevelledMobs] Loading commands
[20:56:05 ERROR]: [LevelledMobs] Error initializing plugin 'LevelledMobs-4.3.1 b112.jar' in folder 'plugins/.paper-remapped' (Is it up to date?)
java.lang.NullPointerException: Cannot invoke "java.lang.reflect.Constructor.newInstance(Object[])" because "io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.pluginCommandNodeConstructor" is null
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.asPluginCommand(PaperCommandRegistration.java:168) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.PaperCommandRegistration.registerCommandNode(PaperCommandRegistration.java:121) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPIBukkit.registerCommandNode(CommandAPIBukkit.java:462) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPIHandler.register(CommandAPIHandler.java:618) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.AbstractCommandAPICommand.register(AbstractCommandAPICommand.java:307) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.CommandAPICommand.register(CommandAPICommand.java:60) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.libs.commandapi.ExecutableCommand.register(ExecutableCommand.java:236) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.commands.CommandHandler.registerCommands(CommandHandler.kt:83) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.commands.CommandHandler.load(CommandHandler.kt:28) ~[LevelledMobs-4.3.1 b112.jar:?]
        at LevelledMobs-4.3.1 b112.jar/io.github.arcaneplugins.levelledmobs.LevelledMobs.onLoad(LevelledMobs.kt:106) ~[LevelledMobs-4.3.1 b112.jar:?]
        at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:59) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.storage.ServerPluginProviderStorage.processProvided(ServerPluginProviderStorage.java:18) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.storage.SimpleProviderStorage.enter(SimpleProviderStorage.java:39) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at io.papermc.paper.plugin.entrypoint.LaunchEntryPointHandler.enter(LaunchEntryPointHandler.java:39) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:567) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:235) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1161) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:308) ~[paper-1.21.5.jar:1.21.5-73-ab0253f]
        at java.base/java.lang.Thread.run(Thread.java:1583) ~[?:?]
[20:56:05 INFO]: [ViaBackwards] Loading server plugin ViaBackwards v5.3.2
[20:56:05 INFO]: Server permissions file permissions.yml is empty, ignoring it
[20:56:05 INFO]: Preparing level "world"
[20:56:06 INFO]: Preparing start region for dimension minecraft:overworld
[20:56:06 INFO]: Preparing spawn area: 0%
[20:56:06 INFO]: Time elapsed: 496 ms
[20:56:06 INFO]: Preparing start region for dimension minecraft:the_nether
[20:56:06 INFO]: Preparing spawn area: 0%
[20:56:06 INFO]: Time elapsed: 217 ms
[20:56:06 INFO]: Preparing start region for dimension minecraft:the_end
[20:56:06 INFO]: Preparing spawn area: 0%
[20:56:07 INFO]: Time elapsed: 61 ms
[20:56:07 INFO]: [ViaVersion] Enabling ViaVersion v5.3.2
[20:56:07 INFO]: [ViaVersion] ViaVersion detected server version: 1.21.5 (770)
[20:56:07 INFO]: [SeeMore] Enabling SeeMore v1.0.2
[20:56:07 INFO]: [LevelledMobs] Enabling LevelledMobs v4.3.1 b112
[20:56:07 INFO]: [LevelledMobs] Building reflection cache, use simple names: true
[20:56:07 INFO]: [LevelledMobs] Using NMS version 1.21.5 for nametag support
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading files...
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading file 'settings.yml'...
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading file 'messages.yml'...
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading file 'externalplugins.yml'...
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading file 'rules.yml'...
[20:56:07 INFO]: [LevelledMobs] Current rules hash: 8c5d8c0b15e7f869b1a603e93863d86cb9c76b7186fb74cc4574de8aaf5263a6
[20:56:07 INFO]: [LevelledMobs] File Loader: Loading file 'customdrops.yml'...
[20:56:07 INFO]: [LevelledMobs] Listeners: Registering event listeners...
[20:56:07 INFO]: [LevelledMobs] Running misc procedures
[20:56:07 INFO]: [LevelledMobs] Tasks: Starting async nametag auto update task...
[20:56:07 INFO]: [LevelledMobs] Start-up complete (took 173ms)
[20:56:07 INFO]: [ViaBackwards] Enabling ViaBackwards v5.3.2
[20:56:07 INFO]: [spark] The spark profiler will not be enabled because it is currently disabled in the configuration.
[20:56:07 INFO]: Done preparing level "world" (1.319s)
[20:56:07 INFO]: Running delayed init tasks
[20:56:07 INFO]: Done (8.792s)! For help, type "help"

[Warriorrrr]

Please report such issues to the plugin authors themselves and not us, the cause behind that error is one of the plugin's dependencies relying on internals (which may change at any time, as shown here).