[Zope] Detecting a NULL Value

I have a field in my MySQL database which is allowed to be null and has a value of NULL as default. I am retrieving this field and numerous others using a call to dtml-in. After the retrieval, I would like to determine what this value is inside my DTML document/method. What is the equivalent of NULL in Zope? Is it a value of 'None'? I am using the following code but it doesn't work. <dtml-if expr="undergraduate_projects_directed == 'None'"> <dtml-call "REQUEST.set('undergraduateProjectsDirected', 'Hello')"> </dtml-if> Any help would be greatly appreciated. Thanks. - Asad