[Zope] setting date to Null in MS SQL?

[Kelley, Sean]

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?