[MC-47850] Cant Make A world

I click classic flat then use preset then i load the world and it gets stuck on Converting World :/so plz fix this #14w06c 😃

Linked issues

Please attach the complete output of the "Development console" which can be found on the second tab of the launcher.

If the launcher closes after game start, please edit your profile and select "Launcher visibility" then, "Keep the launcher open".

What That was not me? why did i get this mail ? o.O