LogicException: The database connection is not serializable, when edit fields with rdf_sync module enabled

I both enabled schemadotorg and rdf_sync modules, and enabled an RDF sync mapping on /admin/structure/types/manage/article (for example), then make some AJAX operations such as changing the cardinality to unlimited on /admin/structure/types/manage/article/fields/node.article.field_image when the error occured the same as this issue 🐛 Error while trying to create a new Entity Reference field Active . The most useful one is probably this one.

After uninstalling either module, the problem dissapeared. I guess it's due to schemadotorg other than rdf_sync.