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Bug description
When stopping a server, a configuration error is shown which may cause the server to hang forever without actually stopping

Steps to reproduce the issue

Expected behavior
For the server to stop cleanly and not hang with errors

Log files

[31Mar2021 15:50:11.462] [Server thread/ERROR] [net.minecraftforge.fml.config.ConfigFileTypeHandler/]: Failed to remove config ./world/serverconfig/gravestone-server.toml from tracker!
java.lang.NullPointerException: null
	at com.electronwill.nightconfig.core.file.FileWatcher.removeWatch(FileWatcher.java:134) ~[core-3.6.2.jar:?]
	at net.minecraftforge.fml.config.ConfigFileTypeHandler.unload(ConfigFileTypeHandler.java:76) ~[forge:?]
	at net.minecraftforge.fml.config.ConfigTracker.closeConfig(ConfigTracker.java:114) ~[forge:?]
	at net.minecraftforge.fml.config.ConfigTracker.lambda$unloadConfigs$2(ConfigTracker.java:88) ~[forge:?]
	at java.lang.Iterable.forEach(Iterable.java:75) ~[?:?]
	at java.util.Collections$SynchronizedCollection.forEach(Collections.java:2067) ~[?:?]
	at net.minecraftforge.fml.config.ConfigTracker.unloadConfigs(ConfigTracker.java:88) ~[forge:?]
	at net.minecraftforge.fml.server.ServerLifecycleHooks.handleServerStopped(ServerLifecycleHooks.java:135) ~[forge:?]
	at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:682) ~[?:?]
	at net.minecraft.server.MinecraftServer.lambda$startServer$0(MinecraftServer.java:232) ~[?:?]
	at java.lang.Thread.run(Thread.java:834) [?:?]

Versions

• Minecraft version 1.16.5
• Forge version 36.0.7
• Mod version 1.9.0

Other mods
Likely occurs with just Gravestones installed, as this is appears to be a standard Forge error

Screenshots (Optional)

Do you have an editor with the config file open or have you deleted the file while the server was running?

I have done neither of those things, I generally attach to the Screen session directly on the server and execute the stop command.

That's weird. Maybe you got something wrong with your file permissions or something. Try removing the config folder and letting it re generate. That should fix file permission issues or open file handles.

Oh, OK, thanks for letting me know!

Thank you for your feedback, it helped me track down the root of the cause: it appears to have been the Performant mod; their latest update must've changed the config file a lot, and it freaks out when trying to write to the old one on server shutdown.
I'll file an issue on their tracker so that people can track down the source of the server hanging easily.