CASE Derived Field help

[abowling]

Hello,
I am using Reportsmith Version 3.10 I need a derived field to do the following:
Look at the termination date field. If it is less than the hire date then make the field null or ' ' else, list the term date.

I have tried several things like below but can't get anything to work.

CASE "employment.term_dt"
WHEN < "employment.hire_dt"
THEN ' ' (i also tried the 'IS NULL')
Else "employment.term_dt
END

 

[ReportSmithing]

case when employment.term_dt < employment.hire_dt then ' '
else employment.term_dt end