Fix default insert on Oracle ( $rs->create({}) with empty hashref )

Fix default insert on Oracle ( $rs->create({}) with empty hashref )

Oracle does not support the INSERT INTO ... DEFAULT VALUES syntax used by
SQLMaker by default. Furthermore, Oracle has no equivalent way of inserting
a row without specifying any columns, so the only reasonably fix seems to
be to pick the first column and supply the DEFAULT keyword as value for it.