Plugin not working on 1.21.4

[Folas1337]

Plugin will throw an error when trying to open a book on version 1.21.4:

[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF] java.lang.ExceptionInInitializerError
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.nbtapi.NBTCompound.setString(NBTCompound.java:176)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.IBook.lambda$getItem$0(IBook.java:196)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.nbtapi.NBT.modify(NBT.java:252)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.IBook.getItem(IBook.java:195)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.IBook.open(IBook.java:165)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.CommandIBooks.onOpen(CommandIBooks.java:85)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/java.lang.reflect.Method.invoke(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.acf.RegisteredCommand.invoke(RegisteredCommand.java:152)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.acf.BaseCommand.executeCommand(BaseCommand.java:578)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.acf.BaseCommand.execute(BaseCommand.java:513)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.acf.RootCommand.execute(RootCommand.java:99)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.acf.BukkitRootCommand.execute(BukkitRootCommand.java:84)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at io.papermc.paper.command.brigadier.bukkit.BukkitCommandNode$BukkitBrigCommand.run(BukkitCommandNode.java:82)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at com.mojang.brigadier.context.ContextChain.runExecutable(ContextChain.java:73)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.execution.tasks.ExecuteCommand.execute(ExecuteCommand.java:31)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.execution.tasks.ExecuteCommand.execute(ExecuteCommand.java:19)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.execution.UnboundEntryAction.lambda$bind$0(UnboundEntryAction.java:8)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.execution.CommandQueueEntry.execute(CommandQueueEntry.java:5)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.execution.ExecutionContext.runCommandQueue(ExecutionContext.java:103)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.Commands.executeCommandInContext(Commands.java:448)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.Commands.performCommand(Commands.java:355)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.Commands.performCommand(Commands.java:342)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.commands.Commands.performCommand(Commands.java:337)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.network.ServerGamePacketListenerImpl.performUnsignedChatCommand(ServerGamePacketListenerImpl.java:2301)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.network.ServerGamePacketListenerImpl.lambda$handleChatCommand$11(ServerGamePacketListenerImpl.java:2275)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.TickTask.run(TickTask.java:18)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:154)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1579)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:207)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:128)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1556)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1549)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:138)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.managedBlock(MinecraftServer.java:1500)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1510)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1346)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:341)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/java.lang.Thread.run(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF] Caused by: java.lang.NullPointerException: Cannot invoke "Object.hashCode()" because "<parameter1>" is null
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/java.util.ImmutableCollections$MapN.probe(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/java.util.ImmutableCollections$MapN.get(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at java.base/java.util.ImmutableCollections$AbstractImmutableMap.getOrDefault(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at io.papermc.paper.pluginremap.reflect.PaperReflection.mapDeclaredFieldName(PaperReflection.java:79)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at io.papermc.reflectionrewriter.runtime.AbstractDefaultRulesReflectionProxy.getDeclaredField(AbstractDefaultRulesReflectionProxy.java:90)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at io.papermc.paper.pluginremap.reflect.PaperReflectionHolder.getDeclaredField(Unknown Source)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      at InteractiveBooks.jar//net.leonardo_dgs.interactivebooks.lib.nbtapi.NBTReflectionUtil.<clinit>(NBTReflectionUtil.java:59)
[20:16:51] [Server thread/ERROR]: [InteractiveBooks] [ACF]      ... 40 more

I suppose it needs to be updated :)