plpgsql

Hi,
I've got two questions about plpgsql. Couldn't find the answer in the 
manual nor anywhere on the net.
Let's say I've got a table A with columns (id integer, txt varchar) and 
a function get_a(integer):
CREATE OR REPLACE FUNCTION get_a(integer) RETURNS a as '
SELECT * FROM a WHERE id=$1;
' LANGUAGE 'sql';

First question: it is possible that a non-existant id will be requested, 
i need the function to return the same thing a normal select would 
return - an empty result set. However I get an error whenever the select 
returns nothing. The error is "Function returning row cannot return null 
value". Is the only solution to this problem to declare function get_a 
to return "SET OF a" ?

Second question I've got a plpgsql function in which I need the result 
of my function get_a.
CREATE OR REPLACE FUNCTION do_stuff(integer) RETURNS integer as '
DECLARE
var a;
...
BEGIN
var := get_a($1);
...
END;
' LANGUAGE 'plpgsql';

I get a syntex error on the line of the assignment (var := get_a($1)). 
IF I replace the assignment with a "select into var * from get_a($1)" 
then everything is ok. It also works with simple types (like varchar, 
integer ant etc.), but not with row-types. Am I missing anything or is 
record assignment not possible in plpgsql?

Thanks in advance,
dim