[Zope] setting date to Null in MS SQL?

I have a simple app where I need to let people set dates to null via a form. I am trying to test for an empty form field and set the value to NULL if empty. It seems to work on form submission but when I do a database query I see it is actually set to 1/1/1900 I have found a way to update a record if it already has a value and you clear the form field, but for some reason this same method does not work for an initial insert. In both of my sql methods I have: <dtml-if "AppDelDate==''"> AppDelDate=NULL, <dtml-else> '<dtml-var name="AppDelDate" sql_quote>', </dtml-if> What am I missing?