title: How do I undo 'git update-ref -d refs/heads/master'?
body: <p>I was attempting a repeated git filter branch which left a final message saying <code>refs/heads/master is unchanged</code>. I read that it was because a backup already existed so I had to get rid of it. So I ran <code>git update-ref -d refs/heads/master</code> and now there are no commits anymore and I can't seem to undo this. Any suggestions? </p>