hibernate-reactive: MS SQL: failure when inserting row if a column has a foreign key constraint

There are many tests in the HR suite using parent/child data. For example: EagerTest.

With MS SQL, these tests fail with:

javax.persistence.PersistenceException: org.hibernate.HibernateException: io.vertx.mssqlclient.MSSQLException: Cannot insert the value NULL into column 'parent_id', table 'master.dbo.Node'; column does not allow nulls. INSERT fails.

I suspect this is due to the column definition:

[Hibernate] create table Node (id int not null, string varchar(255), version int, parent_id int, primary key (id))

Perhaps it should be explicitly declared as NULL