order by...nulls (first|last)

1. Default: sorted as smallest
2. Default: sorted as greatest
3. Default: nulls last
4. Configurable: set default_null_order = [NULLS_FIRST | NULLS_LAST | NULLS_FIRST_ON_ASC_LAST_ON_DESC | NULLS_LAST_ON_ASC_FIRST_ON_DESC]