So I was trying to use apply a diff file to my git dev branch. The diff I wanted to apply was this one here: https://github.com/mbabker/joomla-cms/compare/JHtml_move.patch
I had the same issue.
fatal: git apply: bad git-diff - expected /dev/null on line 96
Or, if I convert all line-endings to Unix format:
error: patch failed: :81 error: : patch does not apply ...
git apply --ignore-whitespace .patch worked with Unix line-endings.
git apply --ignore-whitespace .patch