DBRE generates incorrect mappedBy. The bug seems to be in using foreign key/field sequence:
One the one-2-many side (Course):
@OneToMany(mappedBy = "course")
private Set<Student> Course.students;
On the many-2-one side (Student):
@JoinColumn(name = "ST_CO", referencedColumnName = "CO_PK")
private Course Student.course2;
'mappedBy' should be 'course2' instead of 'course'; OR field 'Student.course2' should be 'Student.course' instead?