Extras field of records should not be None/NULL

[bennybp]

Description

The extras field of base_record (therefore all records) should probably not be null. It's more consistent that it's a dict, even if it's empty.

The original idea is that extras is only populated on record completion. But

• At some point, we might make these settable by the submitter
• We may eventually move to an EAV table, which would always result in an empty dict anyway

This inconsistency has caused problems for some users as well: openforcefield/openff-bespokefit#369 openforcefield/openff-bespokefit#370

Relatively easy fix - make the db column not null, and the pydantic field not optional. A small validator is added to halp newer clients use older servers.

This is backwards compatible - new clients can use old servers, and old clients can still use new servers.

Status

• Code base linted
• Ready to go

[j-wags]

Awesome, thanks Ben!