BUG #1381: invalid input syntax for integer: ""

The following bug has been logged online:

Bug reference: 1381
Logged by: Nicolas Addington
Email address: adding(at)math(dot)wisc(dot)edu
PostgreSQL version: 8.0
Operating system: aix
Description: invalid input syntax for integer: ""
Details:

When a pl/perl trigger for an insert event changes an integer column in the
new row to null, it fails. Interestingly, it doesn't have a problem if the
column was originally null.

create table tbl ( id integer primary key, n integer );

create function trg() returns trigger as $$
undef $_TD->{new}{n};
return 'MODIFY';
$$ language 'plperlu';

create trigger trg before insert on tbl for each row execute procedure
trg();

insert into tbl values (1, null);
INSERT 17997 1

insert into tbl values (2, 0);
ERROR: invalid input syntax for integer: ""