title: Unable to update the work directory using repo
body: <p>I have local project which is a git repository. I have added this local project to Android manifest file. Whenever there is a new commit in my local repository, I am able to fetch my local project using <code>repo sync -n &lt;local project&gt;</code>. However when I try to update the work directory using <code>repo sync -l &lt;local project&gt;</code> I get an error</p>
  
  <blockquote>
    <p>error.GitError: try rev-list ('^0f4e601043d095c8920dad010e5814ef22a20f45', 'HEAD', '--'): fatal: bad object 0f4e601043d095c8920dad010e5814ef22a20f45</p>
  </blockquote>
  
  <p>Can anybody provide pointer to resolve this.</p>