"Unknown biome, defaulting to plains" error upon launching the game

Got the same error while upgrading an 1.15.2 world with --forceUpgrade.

Error is also not very helpfull and leaves me thinking there is now a wrong biome somewhere in the world.

@Kay, I'm pretty sure this has nothing to do with any world file. The message outputs before Minecraft tries to load any file.

@Kay, I'm pretty sure this has nothing to do with any world file. The message outputs before Minecraft tries to load any file.