How to assign an empty value to the date attribute in LAPI?

Mahmoud_Dayeh_(ecead_mad_-_(deleted))

On my VB form if user enters a date in a date field (not mandatory), I assign it to documents date attribute which is not a problem. The problem is when user doesn't enter any value for date field I want documents date attribute to be BLANK but currently it's assigning system date to it by default.does anyone know how to solve this problem??thanks in advance