James Reynolds <james.glenn.reynolds@gmail.com> [Thu, 13 Dec 2018 17:41:06 +0100] rev 4297
issue-6028: resolves 6028 - return (False, ".") instead of (False, '')
Since 4.8, repo[] no longer takes an empty string, so we update to a valid with
similar semantic.
This value is strange and we should probably use an actual node ID here,
however, this is an independent issue.