google-app-engine - Objectify filter on ref

Question

I want have two entities

@Entity
public class User {
   @Index private String email;
   @Index private String name;
   @Index private String age;
     }
 @Entity
public class poll {
     @Index private String pollid;
     @Index private String answer;
     @Index private Ref<User> user;
    }

Now if I want to query poll and filter by email I m getting empty. Is it possible?

ofy().load().type(Poll.class).filter("email", email).list();