rails/rails — pull request #7386 by sishen (2012-08-18 05:14:41+00:00)
Title: ORDER BY xx NULLS first/last will break reverse_sql_order

Oracle and PostgreSQL supports "NULLS first/last" in order by statement. It
will break the reverse_sql_order by concating " DESC" to the order by statement.

For example,

```ruby
User.order("name ASC NULLS FIRST").last
```