Spring Data JPA #OneToOne mapping is not projected - spring-data-jpa

Question

This question is already phrased as an issue here: https://github.com/spring-projects/spring-data-jpa/issues/2369 but for lack of a reaction there I am copying the contents of that issue here, hoping that somebody might find what's wrong with my code or confirm that this could be a bug:
I've set up an example project here that showcases what seems to be a bug in Spring Data projections: https://github.com/joheb-mohemian/gs-accessing-data-jpa/tree/primary-key-join-column-projection-bug/complete
I have a Customer entity that has a OneToOne mapping to an Address entity:
#Entity
public class Customer {
#Id
#GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String firstName;
private String lastName;
#OneToOne(mappedBy = "customer", cascade = CascadeType.ALL)
#PrimaryKeyJoinColumn
private Address address;
//...
}
#Entity
public class Address {
#Id
#Column(name = "customer_id")
private Long id;
#OneToOne
#MapsId
#JoinColumn(name = "customer_id")
private Customer customer;
private String street;
//...
}
Then there are simple projection interfaces:
public interface CustomerProjection {
String getFirstName();
String getLastName();
AddressProjection getAddress();
}
public interface AddressProjection {
String getStreet();
}
But when I try to fetch a projected entity from a repository method like this one:
public interface CustomerRepository extends CrudRepository<Customer, Long> {
//...
<T> T findById(long id, Class<T> type);
}
, getAddress() on the projection will be null, whereas getAddress() when fetching the entity type is populated correctly. Of these two unit tests, only testEntityWithOneToOne()will be successful:
#BeforeEach
void setUpData() {
customer = new Customer("first", "last");
Address address = new Address(customer, "street");
customer.setAddress(address);
entityManager.persist(address);
entityManager.persist(customer);
}
#Test
void testEntityWithOneToOne() {
Customer customerEntity = customers.findById(customer.getId().longValue());
assertThat(customerEntity.getAddress()).isNotNull();
}
#Test
void testProjectionWithOneToOne() {
CustomerProjection customerProjection = customers.findById(customer.getId(), CustomerProjection.class);
assertThat(customerProjection.getAddress()).isNotNull();
}
What's the problem here?