title: "You are on a branch yet to be born" when adding git submodule
body: <p>I am attempting to add a few submodules to my <code>.vim/bundles</code> directory, and when I attempt to add this particular repo Git gives me a strange error I've never seen before:</p>
  
  <pre><code>$ git submodule add -f git://github.com/derekwyatt/vim-scala.git .vim/bundle/vim-scala
  fatal: You are on a branch yet to be born
  Unable to checkout submodule '.vim/bundle/vim-scala'
  </code></pre>
  
  <p>Any idea what can cause this?</p>
  
  <p>If I clone the same repo to a test directory (not through the submodule command), it works fine, and creates the expected files.</p>