JSON: serialize empty arrays to nil

[matthinea]

Problem

In 85ef44b we changed Array types so that empty arrays are serialized to the database as nil. However, we didn't do this for JSON types, which is the type used by nest_many attributes.

Solution

Serialize empty arrays as nil to the database.

For Platform this means that update statements go from this:

UPDATE "places"
SET "document" = ((document - 'primary_contact') || '{"contacts":[],"contacts_count":0,"updated_at":"2024-01-16T23:44:48.913779Z","extended_contacts_count":0}')
WHERE id = '427622700'

to this:

UPDATE "places"
SET "document" = ((((document - 'contacts') - 'contacts_count') - 'primary_contact') || '{"updated_at":"2024-01-17T00:50:33.987526Z","extended_contacts_count":0}')
WHERE id = '427622700'