hibernate - How do you retrieve nested Sets? -

is there annotation i'm missing or limitation hibernate retrieval?

entities:

class {    long id;    set<b> b;     @manytomany(fetch = fetchtype.eager)    @jointable(name = "a_b", joincolumns = @joincolumn(name = "a_id"), inversejoincolumns = @joincolumn(name = "b_id")    public set<b> getbs() {       return b;    }  }  class b {    long id;    set<c> c;     @manytomany(fetch = fetchtype.eager)    @jointable(name = "b_c", joincolumns = @joincolumn(name = "b_id"), inversejoincolumns = @joincolumn(name = "c_id")    public set<c> getcs() {       return c;    }  } 

daos:

class adaoimpl {        public load(long id) {       return new a((a) session.load(a.class, id);    } } 

when attempt load a,

caused by: java.lang.nullpointerexception @ org.hibernate.engine.internal.statefulpersistencecontext.getloadedcollectionownerornull(statefulpersistencecontext.java:853) 

i had issue similar had nested sets, , hashcode methods each showed in stack trace. in hashcode methods, referred each other, removed reference each object in hashcode methods, , no longer got exceptions