title: Git error trying to retrieve log messages
body: <p>I'm trying to lookup all commit messages between two commits, and I'm doing this with a call like:</p>
  
  <pre><code>git --no-pager log --pretty=oneline d875ae4b899411d70ec1d83f8f8d83430fd7d550...4b1d2046c070e82c23d4ced8f089d457f7c5b732
  </code></pre>
  
  <p>This has worked perfectly for months, but recently I started getting the error:</p>
  
  <pre><code>fatal: Invalid symmetric difference expression
  </code></pre>
  
  <p>with no further explanation. Google shows a few bug reports showing this error, but no resolutions. What does this error mean and how do I fix it?</p>