Git error on site install

[Lem]

Hi there,
was trying to install mail_alias via knife cookbook site install mail_alias but got this error:

Removing pre-existing version.
Uncompressing mail_alias version 0.1.0.
removing downloaded tarball
1 files updated, committing changes
ERROR: Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '128'
---- Begin output of git add mail_alias ----
STDOUT: 
STDERR: fatal: Not a git repository: /home/msf/git/chef-repo/.git/modules/cookbooks/mail_alias
---- End output of git add mail_alias ----
Ran git add mail_alias returned 128

After using grep I found that there is a file ".git" (not a dictory!) inside the downloaded tar-Archive with following content:

gitdir: /home/msf/git/chef-repo/.git/modules/cookbooks/mail_alias

I assume that this file is causing my error.