hstore: null value is treated as empty string by avals function

hstore: null value is treated as empty string by avals function

# select avals('gfds'=>null) = array[null], avals('gfds'=>null) =
array[''], version();
?column? | ?column? |
version
----------+----------+------------------------------------------------------------------------------------------------------------------
f | t | PostgreSQL 8.4.4 on x86_64-redhat-linux-gnu,
compiled by GCC gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-46), 64-bit
(1 row)

got f,t
expected t,f
hope the problem is clear

regards,
Alexey