title: Checking if NSDate is valid before usage
body: <p>In my code, I have a UIDatePicker that I use to create new NSDate objects, as well as modify some older ones. One of the things I'd like this UIDatePicker to do would be to load the value of an existing NSDate when you choose to modify it. However, doing so when the existing NSDate* doesn't point to a valid date will cause a crash. Is there some way to check whether the pointer references a valid date before loading it? Thanks for your help. </p>