Marco edited a comment on an issue
Hibernate ORM / Bug HHH-4263
@ManyToMany and @Index
I have trouble adding an index to a column of a table which is part of a many-to-many property mapping. The following example causes a NullPointerException when generating the DDL (the exception can be seen at the end of my post):

@Entity @Table(name="usr")
public class User implements Serializable
{
    @Id @GeneratedValue(strategy=GenerationType.AUTO)
...