[git] fatal: bad default revision 'HEAD'

I got the same error and couldn't solve it.

Then I noticed 3 extra files in one of my directories.

The files were named:

config, HEAD, description

I deleted the files, and the error didn't appear.

config contained:

[core]
    repositoryformatversion = 0
    filemode = true
    bare = true

HEAD contained:

ref: refs/heads/master

description contained:

Unnamed repository; edit this file 'description' to name the repository.