Can't create world with key path that matches an existing level name even if namespace is different

Expected behavior

Should be able to create a world with key key for which Bukkit.getWorld(key) returns null.

Observed/Actual behavior

Some keys fail as a world with that level name already exist.

[09:52:35 ERROR]: Error occurred while enabling Paper-Test-Plugin v1.0.0-SNAPSHOT (Is it up to date?)
java.lang.IllegalArgumentException: Cannot create a world with key plugin:world and name world one (or both) already match a world that exists
	at org.bukkit.craftbukkit.CraftServer.createWorld(CraftServer.java:1152) ~[main/:?]
	at org.bukkit.Bukkit.createWorld(Bukkit.java:767) ~[paper-api-1.18.2-R0.1-SNAPSHOT.jar:?]
	at io.papermc.paper.testplugin.TestPlugin.onEnable(TestPlugin.java:17) ~[test-plugin-1.0.0-SNAPSHOT.jar:?]
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[paper-api-1.18.2-R0.1-SNAPSHOT.jar:?]
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:370) ~[paper-api-1.18.2-R0.1-SNAPSHOT.jar:?]
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:541) ~[paper-api-1.18.2-R0.1-SNAPSHOT.jar:?]
	at org.bukkit.craftbukkit.CraftServer.enablePlugin(CraftServer.java:560) ~[main/:?]
	at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:474) ~[main/:?]
	at net.minecraft.server.MinecraftServer.loadWorld0(MinecraftServer.java:664) ~[main/:?]
	at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:431) ~[main/:?]
	at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:316) ~[main/:?]
	at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1163) ~[main/:?]
	at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:315) ~[main/:?]
	at java.lang.Thread.run(Thread.java:833) ~[?:?]

Steps/models to reproduce

In a plugin onEnable, just run

final NamespacedKey worldKey = new NamespacedKey("plugin", "world");
if (Bukkit.getWorld(worldKey) == null) {
    WorldCreator creator = new WorldCreator(worldKey);
    Bukkit.createWorld(creator);
}

Plugin and Datapack List

none

Paper version

f210f67c4ad1560685e4354dfa242c120e42efe3

Other

No response

Start at CraftServer.createWorld, identified in the stack trace, and compare its handling of the NamespacedKey and world name with Bukkit.getWorld and WorldCreator. Reproduce the case using the TestPlugin.onEnable snippet with a namespaced key whose level name already exists. Done means the namespaced key can create a world when Bukkit.getWorld(key) returns null, while existing-world conflicts remain rejected.