> but I see it was added in 5cfb0a508cf7 as part of support of some MySQL 8 feature

Not really, it was just adapted to also make it work with MySQL 8. The zeroDateTimeBehavior=convertToNull was present before.

The option was present in the original JDBC URL of the person complaining in https://hibernate.atlassian.net/browse/HHH-11396 but it has no value for this test.

I'm going to remove it.