[Crash] net.minecraft.util.crash.CrashException: Saving entity NBT

[A5ho9999]

I finally got around to making this issue which I was meant to since December. Mainly now as a reminder to myself or whoever gets to it first if I don't

This bit needs re-work as it's being cleared before the NBT can be saved. Causing the game to crash (Thankfully most of the game is unaffected and it's just the colours not saving)

 ServerPlayConnectionEvents.DISCONNECT.register((handler, server) -> {
            COLOURS.clear();
        });

Full Error:

net.minecraft.util.crash.CrashException: Saving entity NBT
	at MC/net.minecraft.entity.Entity.writeNbt(Entity.java:1940) ~[server-intermediary.jar:?]
	at MC/net.minecraft.entity.Entity.saveSelfNbt(Entity.java:1858) ~[server-intermediary.jar:?]
	at MC/net.minecraft.entity.Entity.saveNbt(Entity.java:1866) ~[server-intermediary.jar:?]
	at MC/net.minecraft.world.storage.EntityChunkDataAccess.method_31734(EntityChunkDataAccess.java:109) ~[server-intermediary.jar:?]
	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1708) ~[?:?]
	at java.base/java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:762) ~[?:?]
	at MC/net.minecraft.world.storage.EntityChunkDataAccess.writeChunkData(EntityChunkDataAccess.java:107) ~[server-intermediary.jar:?]
	at MC/net.minecraft.server.world.ServerEntityManager.trySave(ServerEntityManager.java:299) ~[server-intermediary.jar:?]
	at MC/net.minecraft.server.world.ServerEntityManager.unload(ServerEntityManager.java:316) ~[server-intermediary.jar:?]
	at MC/net.minecraft.server.world.ServerEntityManager.method_31842(ServerEntityManager.java:394) ~[server-intermediary.jar:?]
	at it.unimi.dsi.fastutil.longs.LongCollection.removeIf(LongCollection.java:274) ~[fastutil-8.5.12.jar:?]
	at MC/net.minecraft.server.world.ServerEntityManager.flush(ServerEntityManager.java:392) ~[server-intermediary.jar:?]
	at MC/net.minecraft.server.world.ServerWorld.save(ServerWorld.java:823) ~[server-intermediary.jar:?]
	at net.minecraft.server.MinecraftServer.save(MinecraftServer.java:556) ~[server-intermediary.jar:?]
	at net.minecraft.server.MinecraftServer.shutdown(MinecraftServer.java:620) ~[server-intermediary.jar:?]
	at MC/net.minecraft.server.dedicated.MinecraftDedicatedServer.shutdown(MinecraftDedicatedServer.java:561) ~[server-intermediary.jar:?]
	at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:735) ~[server-intermediary.jar:?]
	at net.minecraft.server.MinecraftServer.method_29739(MinecraftServer.java:281) ~[server-intermediary.jar:?]
	at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]
Caused by: java.lang.NullPointerException
	at java.base/java.util.ImmutableCollections$ListN.indexOf(ImmutableCollections.java:723) ~[?:?]
	at java.base/java.util.ImmutableCollections$AbstractImmutableList.contains(ImmutableCollections.java:331) ~[?:?]
	at io.ix0rai.rainglow.Rainglow.colourUnloaded(Rainglow.java:89) ~[rainglow-1.3.5+mc1.21.1.jar:?]
	at io.ix0rai.rainglow.Rainglow.getColour(Rainglow.java:110) ~[rainglow-1.3.5+mc1.21.1.jar:?]
	at MC/net.minecraft.entity.passive.AllayEntity.handler$bke000$rainglow$writeCustomDataToNbt(AllayEntity.java:689) ~[server-intermediary.jar:?]
	at MC/net.minecraft.entity.passive.AllayEntity.writeCustomDataToNbt(AllayEntity.java:514) ~[server-intermediary.jar:?]
	at MC/net.minecraft.entity.Entity.writeNbt(Entity.java:1922) ~[server-intermediary.jar:?]
	... 18 more