Ok there isn't really any good reason to give a company like McDonald's free money and yet the QA part of my brain has needed to try this for a long time, so ... I did it.

Using one of the automated tills I ordered a burger with no meat , no ketchup, no pickles, no mustard, no onion and no bread.

It let me put the order through and pay. I got... well nothing. Still at least I satisfied my curiosity if not my appetite.