title: Removing files from git history - bad revision error
body: <p>I am following the instructions on Github (<a href="https://help.github.com/articles/remove-sensitive-data/" rel="noreferrer">https://help.github.com/articles/remove-sensitive-data/</a>) to tidy up a messy repository.  I have successfully cleared out all the .csv files using</p>
  
  <pre><code>git filter-branch --force --index-filter \
  'git rm --cached --ignore-unmatch *.csv' \
  --prune-empty --tag-name-filter cat -- --all
  </code></pre>
  
  <p>And now need to remove all the .docx files.  However, when I use exactly the same command with *.docx instead, I get an error saying:
  <code>fatal: bad revision ' --prune-empty'</code></p>
  
  <p>I pushed to the origin on github, and cloned a fresh copy before doing this second lot of updates.  I'm not sure what I'm doing wrong/differently that is causing this error.  Any help greatly appreciated :)</p>