Create Location fails on PostgreSQL

[uberbrady]

If you try to create a new Location when running on Postgres, you get an error saying something about violating a not-null constraint. While we don't formally support PostgreSQL, we certainly do like to at least try to make it work when we can.

The workaround we had to do for the validation on parent_id is that we had to explicitly set the id to null in the controller method to create the new Location.

MySQL parses that null as "Do the autoincrement". PostgreSQL seems to parse that null as "Try to insert a null into id" and that fails database-level constraint validation.

We've also been talking about some custom validations that might prevent circular location references, this might be a chance to do that, solving two problems at once. I think we have an in-flight PR that might address it - #8253