diff: we can diff to NULL or from NULL.
diff: we can diff to NULL or from NULL.

https://bugzilla.gnome.org/show_bug.cgi?id=702412

GNOME/libgit2-glib,weynhamz/GNOME-libgit2-glib,weynhamz/GNOME-libgit2-glib,weynhamz/GNOME-libgit2-glib,chergert/libgit2-glib,weynhamz/GNOME-libgit2-glib,GNOME/libgit2-glib,chergert/libgit2-glib,chergert/libgit2-glib