pl/pgsql string combining

Dear All

I have 2 table :
1. hotel_pbx_country
2. hotel_pbx_area

Country is one2many to area
Area have a field called "prefx"

The "prefx" field is auto filled by country.code and area.code
and for that purpose, i created trigger and function
--------Trigger-------------
CREATE TRIGGER prefx_xtrigger
BEFORE INSERT OR UPDATE
ON hotel_pbx_area
FOR EACH ROW
EXECUTE PROCEDURE prefx_xupdate();
--------function----------------
CREATE OR REPLACE FUNCTION prefx_xupdate()
RETURNS trigger AS $$
DECLARE ctrcode VARCHAR ;
BEGIN
select code into ctrcode from hotel_pbx_country where "id" =
NEW.country_id ;
NEW.prefx = ctrcode || NEW.code;
RETURN NEW;
END;
$$ LANGUAGE 'plpgsql';
---------------EOF-------------------

I make a bulk entry ,
Not all area have area.code .. it's not mandatory

In normal condition where both country.code and area.code is not null
.... the trigger is work great.
But the problem come when area.code is null, it cause area.prefx to be
NULL also.

Is it normal behavior ? or is it my fault ?

Kindly please give me your enlightment on how to fix it

Sincerely
-bino-