Allow Option::None as null expr in select queries

[angrynode]

Following this comment: angrynode/hightorrent#26 (comment)

I'm sorry i dont understand sea-query architecture to make the PR myself. Though if you point me in the right direction i may be able.

Since inserting None produces null in the DB, I feel like it would be a great addition to allow querying by Option::None.

But maybe there are reasons beyond my comprehension why it's not so. If so, i can make a PR to mention that in the newtype docs, but maybe it should be added elsewhere too.

[tyt2y3]

this is not a limitation, but more a design of SQL such that = NULL is always false, see https://stackoverflow.com/questions/9581745/sql-is-null-and-null

may be we can internally convert eq(None) into is_null(), however I am thinking whether this is "too much magic"

edit: so both Django and Rails does this conversion automatically, which is a strong argument in favour of it

[angrynode]

may be we can internally convert eq(None) into is_null()

That's exactly what i meant.

I personally don't think that's too much magic. Writing raw SQL should not produce magic results, but when selecting from the ORM methods a field value None, i think it should return values produced when inserting None.