title: bad default revision HEAD
body: <p>When I do:
      git log
  , I get message:</p>
  
  <p><code>fatal: bad default revision 'HEAD'</code></p>
  
  <p>, if I do <code>git fsck</code>, I get:</p>
  
  <pre><code>notice: HEAD points to an unborn branch (master)
  Checking object directories: 100% (256/256), done.
  notice: No default references
  dangling blob 965fb7997c335172263ad1e220959ae2c733ed19
  </code></pre>
  
  <p>and <code>git branch</code> gives me empty output.</p>
  
  <p>What is wrong with my repo, and how to fix it?</p>
  
  <p>I tried <code>git symbolic-ref HEAD refs/heads/master</code>, but it didn't help either.</p>