If a differential introduces a new file, then comparing between two diffs on the differential without changes produces the message "This is an empty file. **Show File Contents**".
Possibly introduced by rP10a84d66dbc99130236e3a0de01e9e40e9aceafe. Check out https://secure.phabricator.com/D13626?vs=32925&id=32928&whitespace=ignore-most#9a3a28bd for a current example on this repository.
{F622157}