How to Set a Value to NULL when using Zend_Db

When performing UPDATE and INSERT queries using Zend_Db, I frequently need to set values equal to NULL (not ”). However, the default behavior of Zend_Db::insert() and Zend_Db::update() seems to be that values that are empty are translated into empty strings (”) and put into the database as such.

Does anyone know of way to actually force a NULL value to go into fields if the value is empty in php?

How to Set a Value to NULL when using Zend_Db