ho modifica tutto in HashSet ma mi restituisce un classCastException

codice:
 
javax.ejb.EJBTransactionRolledbackException: java.util.ArrayList cannot be cast to java.util.HashSet
        at org.jboss.ejb3.tx.Ejb3TxPolicy.handleInCallerTx(Ejb3TxPolicy.java:115)
        at org.jboss.aspects.tx.TxPolicy.invokeInCallerTx(TxPolicy.java:130)
        at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:194)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.security.RoleBasedAuthorizationInterceptorv2.invoke(RoleBasedAuthorizationInterceptorv2.java:201)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:186)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:176)
        at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:216)
        at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:207)
        at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:164)
        at $Proxy661.findMazzByFrazionario(Unknown Source)
        at it.poste.tool.persistence.controller.ControllerDao.findByFrazionarioMazzetto(ControllerDao.java:76)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeTarget(MethodInvocation.java:122)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:111)
        at org.jboss.ejb3.EJBContainerInvocationWrapper.invokeNext(EJBContainerInvocationWrapper.java:69)
        at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.invoke(InterceptorSequencer.java:73)

        at org.jboss.ejb3.interceptors.aop.InterceptorSequencer.aroundInvoke(InterceptorSequencer.java:59)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.jboss.aop.advice.PerJoinpointAdvice.invoke(PerJoinpointAdvice.java:174)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.fillMethod(InvocationContextInterceptor.java:72)
        at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_fillMethod_31053739.invoke(InvocationContextInterceptor_z_fillMethod_31053739.java)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor.setup(InvocationContextInterceptor.java:88)
        at org.jboss.aop.advice.org.jboss.ejb3.interceptors.aop.InvocationContextInterceptor_z_setup_31053739.invoke(InvocationContextInterceptor_z_setup_31053739.java)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:62)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.entity.TransactionScopedEntityManagerInterceptor.invoke(TransactionScopedEntityManagerInterceptor.java:56)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.stateless.StatelessInstanceInterceptor.invoke(StatelessInstanceInterceptor.java:68)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.aspects.tx.TxPolicy.invokeInOurTx(TxPolicy.java:79)
        at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:190)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.tx.NullInterceptor.invoke(NullInterceptor.java:42)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.security.RoleBasedAuthorizationInterceptorv2.invoke(RoleBasedAuthorizationInterceptorv2.java:201)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.security.Ejb3AuthenticationInterceptorv2.invoke(Ejb3AuthenticationInterceptorv2.java:186)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:41)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.BlockContainerShutdownInterceptor.invoke(BlockContainerShutdownInterceptor.java:67)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.aspects.currentinvocation.CurrentInvocationInterceptor.invoke(CurrentInvocationInterceptor.java:67)
        at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:102)
        at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:176)
        at org.jboss.ejb3.session.SessionSpecContainer.invoke(SessionSpecContainer.java:216)
        at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:207)
        at org.jboss.ejb3.proxy.impl.handler.session.SessionProxyInvocationHandlerBase.invoke(SessionProxyInvocationHandlerBase.java:164)
        at $Proxy672.findByFrazionarioMazzetto(Unknown Source)
        at it.poste.tool.servlet.findby.FindByFrazMazzetto_srv.processRequest(FindByFrazMazzetto_srv.java:30)
        at it.poste.tool.servlet.findby.FindByFrazMazzetto_srv.doGet(FindByFrazMazzetto_srv.java:55)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:235)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
        at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
        at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
        at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:598)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.HashSet
        at it.poste.tool.persistence.session.VRicercaAggrCodMazzettoFacade.findMazzByFrazionario(VRicercaAggrCodMazzettoFacade.java:57)
Questo è il metodo che ho modificato, naturalmente ho modificato il tipo anche nella servlet:
codice:
 public HashSet<VRicercaAggrCodMazzetto> findMazzByFrazionario(String frazionario) {
        Query q = em.createQuery("SELECT m FROM VRicercaAggrCodMazzetto m WHERE m.frazionario =:frazionario");
            q.setParameter("frazionario", frazionario);
                return (HashSet<VRicercaAggrCodMazzetto>) q.getResultList();
    }