reltime with NULL fields crashes backend

Dmitry Tsitelov (cit(at)tag-ltd(dot)spb(dot)ru) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
reltime with NULL fields crashes backend

Long Description
I use expression like int4(reltime(<interval-field>)) to get interval length in seconds. When <interval-field> is NULL backend crashes (psql session):

organizer=> SELECT reltime(task.duration_real) FROM pmgr_task task WHERE task.id = 5;
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or while processing the request.

#######
OS: FreeBSD 4.1-RELEASE #2
PostgreSQL ver: PostgreSQL 7.0.2 on i386-unknown-freebsdelf4.1, compiled by gcc 2.95.2

####### Postmaster log:

Server process (pid 37685) exited with status 139 at Wed Apr 11 15:33:18 2001
Terminating any active server processes...
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend died abnormally a
nd possibly corrupted shared memory.
I have rolled back the current transaction and am going to terminate you
r database system connection and exit.
Please reconnect to the database system and repeat your query.
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend died abnormally a
nd possibly corrupted shared memory.
I have rolled back the current transaction and am going to terminate you
r database system connection and exit.
Please reconnect to the database system and repeat your query.
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend died abnormally a
nd possibly corrupted shared memory.
I have rolled back the current transaction and am going to terminate you
r database system connection and exit.
Please reconnect to the database system and repeat your query.
Server processes were terminated at Wed Apr 11 15:33:18 2001
Reinitializing shared memory and semaphores
DEBUG: Data Base System is starting up at Wed Apr 11 15:33:18 2001
The Data Base System is starting up
DEBUG: Data Base System was interrupted being in production at Wed Apr 11 15:27
:41 2001
DEBUG: Data Base System is in production state at Wed Apr 11 15:33:18 2001

Sample Code
CREATE TABLE t ( f interval ); : OK
INSERT INTO t (f) VALUES ('23 s'); : OK
SELECT reltime(f) FROM t; : OK
SELECT int4(reltime(f)) FROM t; : OK
DELETE FROM t; : OK
INSERT INTO t (f) VALUES (NULL); : OK
SELECT reltime(f) FROM t; : Backend crash

SELECT reltime(NULL); : OK
SELECT reltime(interval(NULL)); : Backend crash

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