Why does hibernate remove data from association table?

Question

I have following relation in my program:

@Entity
@Table(name = "student")
public class Student extends Person {
    private Map<Document, DocumentInfo> documents =
       new HashMap<Document, DocumentInfo>();
    ...
    @OneToMany
    @JoinTable(name = "student_documents",
            joinColumns = @JoinColumn(name = "student"),
            inverseJoinColumns = @JoinColumn(name = "document_info"))
    @MapKeyJoinColumn(name = "document")
    public Map<Document, DocumentInfo> getDocuments() {
        return documents;
    }
    ...
}

When I save student with his documents information all seems good.. When I read him from database all seems good too, but when I try to read it one more time I have NullPointerException. I did some research and found that during the first invocation of student.getDocuments() hibernate deletes records from table student_documents :

Hibernate: select document0_.id as id2_0_, document0_.title as title2_0_ from document document0_ where document0_.id=?
Hibernate: select document0_.id as id2_0_, document0_.title as title2_0_ from document document0_ where document0_.id=?
Hibernate: delete from student_documents where student=?

What I've done wrong? Thanks

my test code looks like:

    Student student = new Student();
    student.setFirstName("123");
    studentService.add(student);
    Student student2 = studentService.read(student.getId());
    assertFalse(student2.getDocuments().size() == 0); // here it all occurs

service method:

public Student add(Student student) {
    for (Document document : documentRepository.findAll()) {
        DocumentInfo documentInfo = new DocumentInfo(false, "");
        documentInfoRepository.save(documentInfo);
        student.getDocuments().put(document, documentInfo);
    }
    return studentRepository.save(student);
}

Answer 1

Seems like I just found the issue. Can't check it now in my old project, but it's very similar to problems related to this hibernate bug .