I'm pretty sure that there's a property associated with textboxes or dropdown lists, in ASP.NET WebForms, that can substitute a null if the user enters something else. For example we've got users entering "9999" into a field. I'd rather assign a null if the user enters a "9999". Am I correct about that? Or I know that there's an event that can be used to do some processing before submitting the POST to the server. But if there's a property I'd rather just use that.