I have noticed on two occasions that when a customer makes a purchase at my site, if they do not enter their state, then they do not get charged for shipping. I modified my shipping method to include the "no state" checkbox so people will get charged in the future even when a state is not specified, however, I would prefer it if I could simply make it a requirement for them to enter their state before the order is allowed to be processed. Is there a way to make this change?