something simple but I can't

Hi guys,
I trying to return a 0.00 from a function it there are no records found else 
return the amount.

create or replace function danmeans_getpayments(text)
returns numeric as 
$BODY$
declare invoice_num ALIAS FOR $1; _paidamt numeric;

BEGIN select sum(aropen_paid) into _paidamt FROM public.aropen where 
aropen_applyto is not null and (aropen_applyto = $1) ;
       IF (FOUND) THEN         RETURN _paidamt ;END IF;     RETURN 0.00 ;       
END;
$BODY$ LANGUAGE 'plpgsql' VOLATILE COST 100

But all I get is either a blank or the amount paid.  What am I doing wrong???
Johnf