Crash on Launch: FileAlreadyExistsException

When Launching Minecraft 1.13, the Mojang splash screen appears briefly before closing, with the error message "The game crashed whilst initializing game." Showing more details reveals:

 

The game crashed whilst initializing game
Error: java.lang.RuntimeException: java.nio.file.FileAlreadyExistsException: C:\Users\djbut\AppData\Roaming\.minecraft\saves

 

Error log is attached.