NULL as an argument in plpgsql functions

Hi,

this select produces error message:
test=> select test2(NULL);
ERROR: typeidTypeRelid: Invalid type - oid = 0

test2:
CREATE FUNCTION test2 (int4) RETURNS int4 AS '
Declare
keyval Alias For $1;
cnt int4;
Begin
Update hits set count = count +1 where msg_id = keyval;
return cnt;
End;
' LANGUAGE 'plpgsql';

When I do manually update
Update hits set count = count +1 where msg_id = NULL;
it works fine. What's the problem ?

Regards,

Oleg

test=> \d hits
Table = hits
+----------------------------------+----------------------------------+-------+
| Field | Type | Length|
+----------------------------------+----------------------------------+-------+
| msg_id | int4 | 4 |
| count | int4 | 4 |
+----------------------------------+----------------------------------+-------+
test=> select version();
version
------------------------------------------------------------------
PostgreSQL 6.5.2 on i586-pc-linux-gnulibc1, compiled by gcc 2.95.1
(1 row)

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83