diff-valid-unified-empty-line

diff-valid-unified-empty-line is a variable defined in `diff-mode.el'.
Its value is

t

Documentation:
If non-nil, empty lines are valid in unified diffs.
Some versions of diff replace all-blank context lines in unified format with
empty lines. This makes the format less robust, but is tolerated.
See http://lists.gnu.org/archive/html/emacs-devel/2007-11/msg01990.html