When pushing app to heroku: “fatal: Not a git repository”, plus suspected Gemfile changes

I’m trying to push this to heroku https://github.com/gunark/rubycas-server

I ran:

git clone https://github.com/gunark/rubycas-server
bundle install
heroku create
git heroku push master

But I’m getting the following errors. I can’t seem to make sense of them. Any ideas?
It says it’s not a git repo but. And there’s the normal .git directory, etc.

$ git push heroku master
Counting objects: 3563, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (1031/1031), done.
Writing objects: 100% (3563/3563), 686.53 KiB, done.
Total 3563 (delta 2451), reused 3530 (delta 2421)

-----> Heroku receiving push
-----> Ruby/Rack app detected
-----> Gemfile detected, running Bundler version 1.0.7
       Unresolved dependencies detected; Installing...
       Using --without development:test
       fatal: Not a git repository (or any of the parent directories): .git
       You have modified your Gemfile in development but did not check
       the resulting snapshot (Gemfile.lock) into version control

       You have added to the Gemfile:
       * source: source at /disk1/tmp/build_1db9pppnx0kzj
       * activerecord (~> 2.3.12)
       * activesupport (~> 2.3.12)
       * sinatra (~> 1.0)
       * gettext (~> 2.1.0)
       * crypt-isaac (~> 0.9.1)

       You have deleted from the Gemfile:
       * source: source at .

       You have changed in the Gemfile:
       * rubycas-server from `source at /disk1/tmp/build_1db9pppnx0kzj` to `no specified source`
       FAILED: http://devcenter.heroku.com/articles/bundler
 ! Heroku push rejected, failed to install gems via Bundler

To git@heroku.com:rubycas-server.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:rubycas-server.git'

UPDATE: Here’s the result of Quynh Nguyen’s suggestion:

$ git init
Reinitialized existing Git repository in /Users/mm/Documents/Development/thirdparty/rubycas_server/.git/
$ git add .
$ git status
On branch master
nothing to commit (working directory clean)

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