Most databases order tables with the `NULL` value first, having it before
all other data values. Postgres has `NULLS` last.

Fortunately, ANSI SQL has an option to allow the database to specify where NULLS
come out in this sort order

    ORDER BY column ASC NULLS FIRST

MS SQL, SQLite, Oracle, and Postgres all follow this syntax. Unfortunately, MySql
does not.

Before:

PostgreSQL: both `.nulls_first()` and `.nulls_last()` work as designed.
Others: both raise a runtime error.

After:

MySQL: `.nulls_first()` works as designed.
MySQL: `.nulls_last()` raises a runtime error
Others: both work as designed