Blank data entry that are really numeric

HI -I have a screen that displays a dates from and to, to the user. It is 
defined as a date type ?M?,w/ Mand. Entry. Zeros are allowed to be entered as a 
lower and/or upper limit. The problem is that when the user just hits enter, it 
was generating a data decimal error, as the field is rearranged in a data 
structure including making it numeric, and then processed. I would like such an 
occurance to be handled by the DSPF, or earlier in the program What I did was 
check the fields prior to their being processed and if both are blank I exit 
the subroutine. I am sure there is a much cleaner and better way to do this. 
Please let me in on this.
Thanks,
Rob