title: warning: remote HEAD refers to nonexistent ref, unable to checkout. and no branches found
body: <p>I'm trying to checkout libvpx but I get the error below. </p>
  
  <pre><code>sudo git clone http://git.chromium.org/webm/libvpx.git
  Initialized empty Git repository in /opt/ffmpeg/sources/libvpx/.git/
  warning: remote HEAD refers to nonexistent ref, unable to checkout.
  cd libvpx/
  git branch -a
  &lt;nothing&gt;
  </code></pre>
  
  <p>I've even tried to checkout the master branch specifically but still nothing. </p>
  
  <pre><code>sudo git clone http://git.chromium.org/webm/libvpx.git -b master
  Initialized empty Git repository in /opt/ffmpeg/sources/libvpx/.git/
  warning: Remote branch master not found in upstream origin, using HEAD instead
  warning: remote HEAD refers to nonexistent ref, unable to checkout.
  </code></pre>