XDoclet - Composite-id

Hi, I'm trying to create a compost primary key and this error is
raised:

SEVERE: Invoking method failed:
xdoclet.modules.hibernate.HibernateTagsHandler.ifHasCompositeId,
line=169 of template file
....
Caused by: java.lang.NullPointerException

My code:

public class AcessoId implements Serializable{

// <editor-fold defaultstate="collapsed" desc=" Property: String
id_usuario ">
private String id_usuario;
/**
* @hibernate.property
* column="id_usuario"
* @hibernate.column
* name="id_usuario"
*/
public String getId_usuario() {
return id_usuario;
}
public void setId_usuario(String id_usuario) {
this.id_usuario = id_usuario;
}
// </editor-fold>

// <editor-fold defaultstate="collapsed" desc=" Property: String
cod_sist ">
private String cod_sist;
/**
* @hibernate.property
* column="cod_sist"
* @hibernate.column
* name="cod_sist"
*/
public String getCod_sist() {
return cod_sist;
}
public void setCod_sist(String cod_sist) {
this.cod_sist = cod_sist;
}
// </editor-fold>
}

package custom.entities ;
/**
*
*
* @hibernate.class
* table="acesso"
*
*/
public class Acesso {

// <editor-fold defaultstate="collapsed" desc=" PrimaryKey:
custom.entities.AcessoId acessoId ">
private custom.entities.AcessoId acessoId;
/**
* @hibernate.id
* generator-class="assigned"
*/
public custom.entities.AcessoId getAcessoId () {
return acessoId;
}
public void setAcessoId (custom.entities.AcessoId acessoId) {
this.acessoId = acessoId;
}
//</editor-fold>

}
What's happening?

Thank's