A QA engineer walks into a bar, and orders a beer. Then he orders 0 beers. Then he orders 999999999999 beers. Then he orders an aardvark. Then he orders nothing. Then he orders -1 beers. Then he orders NULL beers. Then he orders asnwikfjsdf. Then he orders a ""><script>give_me_your_credit_card()</script>. Finally, the QA engineer leaves without paying, comes back, and asks for the tab.