A date parsing utility function in the ORM (https://github.com/bookbrainz/bookbrainz-data-js) considers that if year is 0 it should return a null date instead.
Here's the culprit:
https://github.com/bookbrainz/bookbrainz-data-js/blob/1d36915dcd5b895c6860048d8051a79784618967/src/util.js#L178-L180

If year=0, `!year` will equal true, and return `null`

This should be changed to allow for year=0 somehow.