i finally figured it out... so i thought i would come back and post the answer so that it may help someone else someday. here's the correct way (showing only the body of the trigger):

WHEN (NU.SPEC_PERM <> ' ')
BEGIN ATOMIC
SET NU.OPTIN_DT =
CASE
WHEN NU.SPEC_PERM = 'Y'
THEN CURRENT DATE
ELSE NULL
END,
NU.OPTOUT_DT =
CASE
WHEN NU.SPEC_PERM = 'N'
THEN CURRENT DATE
ELSE NULL
END;
END ?