Select into table%ROWTYPE failed

I´m testing a trigger function in a 9.4 installation.
It´s for bill number assignation, but with a twist: there are various 
numbering ranges. This ranges are defined by a text code, a minimum and 
maximum. Every bill have some code taken from the set defined in a 
specific table (billnumberrange)
The first approach was the obvious "select into" a row instance, using 
table%ROWTYPE as the destination.
That failed, leaving all fields of the  instance as null.
But selecting into the interesting fields works ok. The trigger function 
follows; the initial approach lines are commented.

CREATE FUNCTION nextbillnumber() RETURNS trigger
     LANGUAGE plpgsql
     AS $$
DECLARE
   lastnumber integer;
   lowerlimit integer;
   upperlimit integer;
   -- ranger billnumberrange%ROWTYPE;
BEGIN
   if NEW.billnumber = 0 THEN
       select billnumberrange.lowerlimit, billnumberrange.upperlimit 
from billnumberrange
         where billnumberrange.groupcode = NEW.groupcode into 
lowerlimit, upperlimit;
         --where billnumberrange.groupcode = NEW.groupcode into ranger;
         -- RAISE NOTICE 'first select result % % <> %', 
ranger.groupcode, ranger.lowerlimit, ranger.upperlimit; this NOTICE 
showed <NULL> <NULL> <> <NULL>
        RAISE NOTICE 'first select result % <> %', lowerlimit, 
upperlimit;-- this shows the expected values
        select max(billnumber) from bill
         where billnumber BETWEEN lowerlimit and upperlimit
         --  where billnumber BETWEEN ranger.lowerlimit and 
ranger.upperlimit
         into lastnumber;
     RAISE NOTICE 'second select result %', FOUND;
     if lastnumber is null THEN
         lastnumber := lowerlimit;
         -- lastnumber := ranger.lowerlimit;
     end if;
     RAISE NOTICE 'lastnumber is %', lastnumber;
     NEW.billnumber = lastnumber + 1;
   end if;
   return NEW;
END;
$$;

What was wrong in the first approach?
TIA


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