Context

My plugin does the following:

• Copy a world folder into the root directory

• * Load the world-

• Teleport the player into the world
• Let the player do things in the world until he leaves
• Unload the world, save it elsewhere and delete the world folder in the root directory

The first three things happen in the same tick.

The problem

Even though the world loads without issues for the first time, after unloading it and loading a newly copied one with the same name, teleporting the player into it causes an NPE.

Checking blocks, getting locations etc. in the world works without problems, and debbuging the plugin prints the target location in the newly loaded world as "Location{world=CraftWorld

[19:28:54] [Server thread/INFO]: Location{world=CraftWorld

,x=80.0,y=4.0,z=192.0,pitch=0.0,yaw=0.0}
[19:28:54] [Server thread/ERROR]: null
org.bukkit.command.CommandException: Unhandled exception executing command 'dxl' in plugin DungeonsXL v0.18-SNAPSHOT
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:47) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:149) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at org.bukkit.craftbukkit.v1_15_R1.CraftServer.dispatchCommand(CraftServer.java:723) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.PlayerConnection.handleCommand(PlayerConnection.java:1658) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.PlayerConnection.a(PlayerConnection.java:1498) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.PacketPlayInChat.a(PacketPlayInChat.java:47) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.PacketPlayInChat.a(PacketPlayInChat.java:1) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.PlayerConnectionUtils.lambda$0(PlayerConnectionUtils.java:19) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.TickTask.run(SourceFile:18) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeTask(SourceFile:144) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandlerReentrant.executeTask(SourceFile:23) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.executeNext(SourceFile:118) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.MinecraftServer.ba(MinecraftServer.java:918) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.MinecraftServer.executeNext(MinecraftServer.java:911) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.IAsyncTaskHandler.awaitTasks(SourceFile:127) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.MinecraftServer.sleepForTick(MinecraftServer.java:895) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at net.minecraft.server.v1_15_R1.MinecraftServer.run(MinecraftServer.java:828) [spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at java.lang.Thread.run(Thread.java:748) [?:1.8.0_241]
Caused by: java.lang.NullPointerException
at net.minecraft.server.v1_15_R1.PlayerList.moveToWorld(PlayerList.java:644) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at org.bukkit.craftbukkit.v1_15_R1.entity.CraftPlayer.teleport(CraftPlayer.java:672) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at org.bukkit.craftbukkit.v1_15_R1.entity.CraftEntity.teleport(CraftEntity.java:453) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
at de.erethon.commons.player.PlayerUtil.secureTeleport(PlayerUtil.java:89) ~[?:?]
at de.erethon.dungeonsxl.player.DEditPlayer.<init>(DEditPlayer.java:62) ~[?:?]
at de.erethon.dungeonsxl.command.EditCommand.onExecute(EditCommand.java:81) ~[?:?]
at de.erethon.commons.command.DRECommandExecutor.onCommand(DRECommandExecutor.java:67) ~[?:?]
at org.bukkit.command.PluginCommand.execute(PluginCommand.java:45) ~[spigot-1.15.2.jar:git-Spigot-a03b1fd-fc318cc]
... 17 more

The NPE occurs at this line in PlayerList:

location.setWorld(server.getWorldServer(dimensionmanager).getWorld());

If the server code is stretched like this:

644 location.

645 setWorld(

646 server

647 .getWorldServer(dimensionmanager)

648 .getWorld());

the NPE occurs at line 648, so getWorldServer(dimensionmanager) must be null for some reason.

Plugin source: https://github.com/DRE2N/DungeonsXL/blob/master/core/src/main/java/de/erethon/dungeonsxl/player/DEditPlayer.java (the version used for this has three printlns between 57 and 58) and https://github.com/DRE2N/DRECommons/blob/master/core/src/main/java/de/erethon/commons/player/PlayerUtil.java#L78

I hope you can help, thank you for all of the good work so far

Edit: It turned out I messed up at some point and kept a reference to a World object when the World was already unloaded.