Read empty Date from NAV through SQL

Hi,

I am trying to look for a record in NAV through SQL .. primary key consists of 4 fields, one of which is a date. What value should I pass through SQL to be able to search for a record with the date field empty? I have tried empty string, 0D, January 1, 1753, 00:00:00.000 (the earliest permitted DateTime).

Thanks, in advance!
Y_1716