pl/pgsql NEW variable substitution

i want to check in a trigger if certain columns are not left empty. The
columns i have to check are stored in another table. How do i do the
following

BEGIN
SELECT INTO col_record * FROM modules WHERE type_module_id =
NEW.type_module_id AND is_afsluit_kolom;
IF NOT FOUND THEN
RAISE EXCEPTION 'geen afsluitkolom gedefinieerd voor type_module % ',
NEW.type_module_id;
ELSE
col_naam := col_record.kolom_naam;
RAISE NOTICE 'kolom to check is % ', col_naam;
--- check if afsluitrecord is empty
IF NEW.col_naam != '' THEN
RETURN NEW;
ELSE
RAISE EXCEPTION 'dit record is afgesloten voor wijzigingen !';
END IF;
END IF;
END;

I want col_naam to be evaluated before used with NEW . Now i get a
warning that the table the trigger is written for doesn't has a column
'col_naam'.

jef peeraer