9.1 plperlu bug with null rows in trigger hash

I've not been able to duplicate this in a standalone script yet,
but in the guts of Bucardo is a trigger function called validate_goat()
that is giving this error on 9.1 HEAD, but not on previous versions:

"Failed to add table "public.pgbench_tellers": DBD::Pg::st execute
failed: ERROR: Modification of non-creatable hash value attempted,
subscript "pkey" at line 4."

I was able to simplify the function to just this and still produce
the error:

CREATE OR REPLACE FUNCTION bucardo.validate_goat()
RETURNS TRIGGER
LANGUAGE plperlu
AS
$bc$

my $new = $_TD->{new};
$new->{pkey} = 'foobar';

return 'MODIFY';

$bc$;

It's used like this:

CREATE TRIGGER validate_goat
BEFORE INSERT OR UPDATE ON bucardo.goat
FOR EACH ROW EXECUTE PROCEDURE bucardo.validate_goat();

The goat table has many text fields, of which one is
pkey. Setting it to any of those other columns will cause the error.
However, setting it to a text field that is NOT NULL DEFAULT will
*not* produce the error, so obviously something is setting
$_TD->{new}{somecol} to undef in the wrong way. I'm baffled as
to why I cannot reproduce it standalone, but wanted to get the
bug out there so I don't forget about it and in case anyone
wants to take a swing at it. Some Googling suggests it might
be because we are using &PL_sv_undef instead of a proper
newSV(0).

--
Greg Sabino Mullane greg(at)endpoint(dot)com
End Point Corporation
PGP Key: 0x14964AC8