Yeah.. so, Autotune states that it shouldn't be blank because it's a "required" field by Facebook. However, it actually can be blank and Facebook currently does not have any issues with that. We just like to really point it out to users that Facebook does state it's required so it *should* be set.
At some point, they may disable apps or do something else if you haven't specified the Privacy URL. You never know
Either way, glad you got it, and should you need anything else, just let us know!
Thanks,
Alex