Set null or optional date

We would like the ability to set a datetime to null or have the datetime pickers be optional. At the moment we have a few optional date fields in a form but they always default to datetime.now unless you set it to a New DateTime(), in which case it'll default to 1/01/0001. This then has to be handled later to check if a new date has been entered or not. Alternatively an arbitrary date can be set but that's also an issue as you have to again handle if there has been a change of date or not. Having it nullable with the datetime calendar picker defaulting to today or the current month would make things easier.