When trying to create / load a new world with a multi-world plugin (such as Multiverse-Core, TARDIS) the server returns an error:

net.minecraft.server.v1_14_R1.ResourceKeyInvalidException: Non [a-z0-9/._-] character in path of location: minecraft:TARDIS_TimeVortex

This happens if using the default generator or a custom generator.

Code to reproduce:

WorldCreator.name("Test_World").type(WorldType.NORMAL).environment(World.Environment.NORMAL).createWorld();

Bug reproduction plugin and server log attached.