How can I create null value from function call with no results?

The following simplified snippet demonstrates the behaviour I'm trying to change:


create or replace function test_empty_row(p_instance_id integer)
RETURNS TABLE (instance_id_int INTEGER,  valstring TEXT)
AS
$$
BEGIN
return query SELECT 0, 'nothing'::text where 1 = 2;
END;   
$$ LANGUAGE plpgsql;

select 1,test_empty_row(1);   (this is actually "SELECT A.somefield, myfunc(A.somefield) from my_table A" in my code)