No longer able to create worlds not in the (default) minecraft namespace

[xt449]

Expected behavior

In Paper 1.21.x, it was possible to create worlds with a given namespace other than "minecraft".

Observed/Actual behavior

In the 26.1.x alpha builds. This is no longer possible and instead throws UnsupportedOperationException: Custom world keys not yet implemented
Even though there is deprecation warning or otherwise.

Steps/models to reproduce

new org.bukkit.WorldCreator("level_name", new org.bukkit.NamespacedKey("namespace", "level_name");
// or
new org.bukkit.WorldCreator(new org.bukkit.NamespacedKey("namespace", "level_name");

Plugin and Datapack List

N/A

Paper version

26.1.1-14-dev/26.1@f6d2701

Other

See:

Paper/paper-api/src/main/java/org/bukkit/WorldCreator.java

Line 61 in 2d6e82e

throw new UnsupportedOperationException("Custom world keys not yet implemented");