This is how i have been dealing with empty form fields:

# If certain fields are blank, then give a "blank form" response
&missing_info_error ("Date") unless $FORM{'date'};
&missing_info_error ("Name") unless $FORM{'name'};
&missing_info_error ("Eng/Rig") unless $FORM{'engorrig'};
&missing_info_error ("Engine Model") unless $FORM{'em'};
&missing_info_error ("Test Stand or Build Cell") unless $FORM{'tsbc'};
&missing_info_error ("Time Lost") unless $FORM{'tl'};

Originally posted as a Categorized Answer.