Minecraft crashes when creating a new world

This was how the crash happened: First, I went to create a new world. Then I went to "More World Options..." After that, I made the world type as superflat and allowed cheats to be on. Then, I clicked "Done." Next, I made the game mode to creative. Then I went back to "More World Options..." to make sure cheats was still on. From there I clicked "Create New World" and then it started to make the new world. When it was about to be done, it crashed.