Missing support for order by nulls first/last

[erwinw]

Several database engines (PostgreSQL, Oracle, Sqlite, H2) have implemented support for SQL:2003's ORDER BY myField ASC NULLS FIRST syntax, that is to say, the ability to explicitly control whether NULL values should be sorted first or last.

Unfortunately, at the moment Exposed only supports the basic ASC and DESC options. While it is possible to create work-arounds, this is a rather hack-y approach.