function problems

I am trying to write a postgres function and I'm getting errors when
the parameter sub is empty (it wont ever be null) and meetCode has a number.

This is the function code:

create or replace function SubjectDisplay(IN subj varchar,IN meetCode
numeric,IN meetTrWP integer,OUT Display varchar)

returns varchar as
$BODY$
Declare
    meetType varchar;
BEGIN
    IF subj='' Then
        if meetCode=0 Then
            if meetTrWp=0 Then
                Select S_MEETING_TITLE as Display from System Limit 1;
                Return;
            elseif meetTrWp=1 Then
                Select S_TRAINING_TITLE as Display from System Limit 1;
                Return;
            else
                Select S_WP_TITLE as Display from System Limit 1;
                Return;
            end if;
        else
            --This is where I run into problems. I get an error when I run it.
Query has no destination for result data
            Select MT_DESCRIPTION as meetType from MEETING_TYPE Where MT_CODE=meetCode;
            Display := meetType
            Return;
        end if;
    else
        Display := subj
        Return;
    end if;

    Return;
END;

$BODY$
LANGUAGE plpgsql IMMUTABLE
COST 100;

Christine Penner