Erro no hibernate

Pessoal,

Estou fazendo um relacionamento muitos para muitos no Hibernate assim:

<set name=“vinculacao” table=“VINCULACAO”>

<key column=“ID_VINCULACAO”/>

<many-to-many

column="ID_CENTRO_CUSTO"

class=“admin.modelo.negocio.CentroCustoObjNeg” />

</set> e está dando este erro:

Mapping class:admin.modelo.negocio.UgObjNeg -> UG

10:25:27,489 INFO  [Binder] Mapping collection: admin.modelo.negocio.UgObjNeg.vinculacao -> VINCULACAO

10:25:27,505 ERROR [STDERR] java.lang.NullPointerException

10:25:27,505 ERROR [STDERR] 	at core.persistencia.APIPersistencia.<init>(Unknown Source)

10:25:27,505 ERROR [STDERR] 	at admin.modelo.servico.SgpFacadeBean.ejbCreate(Unknown Source)

10:25:27,505 ERROR [STDERR] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

10:25:27,505 ERROR [STDERR] 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

10:25:27,505 ERROR [STDERR] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

10:25:27,505 ERROR [STDERR] 	at java.lang.reflect.Method.invoke(Method.java:324)