how do i insert an empty string ?

FAQ: A search yielded nothing explicit...

I have an INSERT statement:

INSERT INTO metadata (md5, origin, name, value)
VALUES ('fd859f263bd0579935f2146a22d24f32', 'EXIF',
'UserComment', '')

but this fails (using Perl DBI, DBD::Pg) because $dbh->quote() returns two
single quotes, which fails because something along the way thinks this is a
single quote. I do NOT want to insert a NULL but an empty string...

(This is either doing a $dbh->do(...) or a prepare ... execute without
$dbh->quote())

Peter