plpgsql and triggers

I'm looking for a way to use a parameter given to a trigger function as fieldname. It should be something like

create function f_makeupper() returns trigger as '

begin

    NEW.TG_ARGV[0] := upper(NEW.TG_ARGV[0]);

    RETURN NEW;

end;

' language 'plpgsql';

create trigger "TRIG_tbltest" before insert on tbltest for each row execute procedure f_makeupper("fieldname");

 

I can create both the function and the trigger, but on inserting a new record I get an error telling me that "record 'new' has no field 'tg_argv'"

 

What am I doing wrong ?