NULL Date Entries...

In one of my forms, I am building a variable that I can use as an INSERT string. On my form, I have several DATE fields which exist of 3 fields MM - DD - YYYY when I build my string it looks like this: array('dbf'=>'applicant_dob', 'f'=>array('applicant_dob_1','applicant_dob_2','applicant_dob_3'), 'req'=>0, 's'=>'/'), This enters in the DB fine when there is a DATE, but when these fields are left empty, it inserts into the the DB as 2069-12-31. How does one deal with this? Don Wieland