Seen in https://secure.phabricator.com/differential/changeset/?ref=187337%2F187324&whitespace=ignore-all
It says "This file contains generated code, which does not normally need to be reviewed. Show File Contents"
It does not say that there were no changes (but I assume there were none in this case), and when you click "Show File Contents" you get just "Show First 20 Lines • Show All 6325 Lines • Show Last 20 Lines" rather than showing you the file contents.