On Mon, Oct 13, 2014 at 8:14 AM, John Chilton <jmchilton@gmail.com> wrote:

My understanding is that it was briefly optional (and maybe just
through the API) but that was a bug. I think Dannon made that fix a
few months ago. Sorry for the confusion.

This is correct, public usernames are required and there was a bug that was incorrectly validating empty ones.