pg_catalog.pg_get_serial_sequence() returns NULL

Hi!

I use PG 8.1.5

I execute in psql next comands:

create table t_table (gid serial, name varchar);

select pg_catalog.pg_get_serial_sequence('t_table', 'gid');
pg_get_serial_sequence
------------------------
public.t_table_gid_seq

create table t_table_1() inherits (t_table);

\d t_table_1
Table "public.t_table_1"
column | Type | Модификаторы
---------+-------------------+-------------------------------------------------------
gid | integer | not null default
nextval('t_table_gid_seq'::regclass)
name | character varying |
Inherit: t_table

select pg_catalog.pg_get_serial_sequence('t_table_1', 'gid');
pg_get_serial_sequence
------------------------
<NULL>

How I can get name of sequence used by gid column of partition table? And
why for t_table_1 pg_get_serial_sequence() returns NULL?
It returns NULL also if I create new sequence manually and use ALTER TABLE
ALTER COLUMN <column> SET DEFAULT nextval(<my_new_sequence>::regclass).

In http://www.postgresql.org/docs/8.1/static/datatype.html#DATATYPE-SERIAL I
can read that type SERIAL is equivalent to

CREATE SEQUENCE *tablename*_*colname*_seq;
CREATE TABLE *tablename* (
*colname* integer DEFAULT nextval('*tablename*_*colname*_seq') NOT NULL
);

Thanks in advance

Sergey Karin