JPA ponteiro nulo

public EntityManager getEntityManager(){
       if( emf == null )
           emf = Persistence.createEntityManagerFactory( "PWEBPU" );
       return emf.createEntityManager();
    }

public void init() {
        // Perform initializations inherited from our superclass
        super.init();
        // Perform application initialization that must complete
        // *before* managed components are initialized
        // TODO - add your own initialiation code here
        
        // <editor-fold defaultstate="collapsed" desc="Managed Component Initialization">
        // Initialize automatically managed components
        // *Note* - this logic should NOT be modified
        try {
            _init();
        } catch (Exception e) {
            log("index Initialization Failure", e);
            throw e instanceof FacesException ? (FacesException) e: new FacesException(e);
        }
        
        // </editor-fold>
        // 

         EntityManager em = getSessaoBean().getEntityManager();
}

[TopLink Config]: 2007.05.24 08:51:12.032--ServerSession(26914410)--Connection(30859913)--connecting(DatabaseLogin(
        platform=>PostgreSQLPlatform
        user name=> ""
        connector=>JNDIConnector datasource name=>jdbc/professor
))
[TopLink Config]: 2007.05.24 08:51:12.066--ServerSession(26914410)--Connection(32967261)--Connected: jdbc:postgresql://10.1.1.1:5432/PROFONLINE?loginTimeout=0&prepareThreshold=0
        User: cassio
        Database: PostgreSQL  Version: 8.1.9
        Driver: PostgreSQL Native Driver  Version: PostgreSQL 8.2 JDBC4 with SSL (build 504)
[TopLink Config]: 2007.05.24 08:51:12.071--ServerSession(26914410)--Connection(29984942)--connecting(DatabaseLogin(
        platform=>PostgreSQLPlatform
        user name=> ""
        connector=>JNDIConnector datasource name=>jdbc/professor
))
[TopLink Config]: 2007.05.24 08:51:12.076--ServerSession(26914410)--Connection(2919088)--Connected: jdbc:postgresql://10.1.1.1:5432/PROFONLINE?loginTimeout=0&prepareThreshold=0
        User: cassio
        Database: PostgreSQL  Version: 8.1.9
        Driver: PostgreSQL Native Driver  Version: PostgreSQL 8.2 JDBC4 with SSL (build 504)
[TopLink Config]: 2007.05.24 08:51:12.114--ServerSession(26914410)--Connection(1044101)--disconnect
[TopLink Info]: 2007.05.24 08:51:12.125--ServerSession(26914410)--file:/home/cassio/Projetos/Web/ProfessorOnLine/build/web/WEB-INF/classes-PWEBPU logout successful
WebModule[/ProfessorOnLine] ServletContext.log():null
executePhase(RENDER_RESPONSE 6,com.sun.faces.context.FacesContextImpl@1f24008) threw exception
com.sun.rave.web.ui.appbase.ApplicationException
        at com.sun.rave.web.ui.appbase.faces.ViewHandlerImpl.cleanup(ViewHandlerImpl.java:559)
        at com.sun.rave.web.ui.appbase.faces.ViewHandlerImpl.renderView(ViewHandlerImpl.java:276)
        at com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:133)
        at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:244)
        at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:140)
        at javax.faces.webapp.FacesServlet.service(FacesServlet.java:245)
        at org.apache.catalina.core.ApplicationFilterChain.servletService(ApplicationFilterChain.java:397)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:184)
        at com.sun.webui.jsf.util.UploadFilter.doFilter(UploadFilter.java:203)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:216)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:184)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:368)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:216)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:184)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:276)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:566)
        at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:536)
        at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:240)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:179)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:566)
        at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:73)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:182)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:566)
        at com.sun.enterprise.web.VirtualServerPipeline.invoke(VirtualServerPipeline.java:120)
        at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:939)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:137)
        at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:566)
        at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:536)
        at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:939)
        at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:239)
        at com.sun.enterprise.web.connector.grizzly.ProcessorTask.invokeAdapter(ProcessorTask.java:667)
        at com.sun.enterprise.web.connector.grizzly.ProcessorTask.processNonBlocked(ProcessorTask.java:574)
        at com.sun.enterprise.web.connector.grizzly.ProcessorTask.process(ProcessorTask.java:844)
        at com.sun.enterprise.web.connector.grizzly.ReadTask.executeProcessorTask(ReadTask.java:287)
        at com.sun.enterprise.web.connector.grizzly.ReadTask.doTask(ReadTask.java:212)
        at com.sun.enterprise.web.connector.grizzly.TaskBase.run(TaskBase.java:252)
        at com.sun.enterprise.web.connector.grizzly.WorkerThread.run(WorkerThread.java:75)
Caused by: java.lang.NullPointerException
        at oracle.toplink.essentials.platform.database.PostgreSQLPlatform.platformSpecificSequencingInitialization(PostgreSQLPlatform.java:413)
        at oracle.toplink.essentials.internal.sequencing.SequencingManager.onConnect(SequencingManager.java:568)
        at oracle.toplink.essentials.internal.sessions.DatabaseSessionImpl.initializeSequencing(DatabaseSessionImpl.java:137)
        at oracle.toplink.essentials.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:371)
        at oracle.toplink.essentials.internal.sessions.DatabaseSessionImpl.initializeDescriptors(DatabaseSessionImpl.java:360)
        at oracle.toplink.essentials.internal.sessions.DatabaseSessionImpl.postConnectDatasource(DatabaseSessionImpl.java:677)
        at oracle.toplink.essentials.internal.sessions.DatabaseSessionImpl.loginAndDetectDatasource(DatabaseSessionImpl.java:559)
        at oracle.toplink.essentials.ejb.cmp3.EntityManagerFactoryProvider.login(EntityManagerFactoryProvider.java:180)
        at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:230)
        at oracle.toplink.essentials.internal.ejb.cmp3.base.EntityManagerFactoryImpl.getServerSession(EntityManagerFactoryImpl.java:78)
        at oracle.toplink.essentials.internal.ejb.cmp3.base.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:113)
        at oracle.toplink.essentials.internal.ejb.cmp3.base.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:107)
        at oracle.toplink.essentials.internal.ejb.cmp3.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:76)
        at br.gdcom.web.SessaoBean.getEntityManager(SessaoBean.java:235)
        at br.gdcom.web.user.index.init(index.java:221)
        at com.sun.rave.web.ui.appbase.servlet.LifecycleListener.fireInit(LifecycleListener.java:555)
        at com.sun.rave.web.ui.appbase.servlet.LifecycleListener.attributeAdded(LifecycleListener.java:405)
        at org.apache.coyote.tomcat5.CoyoteRequest.setAttribute(CoyoteRequest.java:1634)
        at org.apache.coyote.tomcat5.CoyoteRequestFacade.setAttribute(CoyoteRequestFacade.java:522)
        at javax.servlet.ServletRequestWrapper.setAttribute(ServletRequestWrapper.java:295)
        at javax.servlet.ServletRequestWrapper.setAttribute(ServletRequestWrapper.java:295)
        at com.sun.faces.context.RequestMap.put(ExternalContextImpl.java:1055)
        at com.sun.faces.application.ApplicationAssociate.createAndMaybeStoreManagedBeans(ApplicationAssociate.java:525)
        at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:82)
        at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:143)
        at com.sun.faces.el.FacesCompositeELResolver.getValue(FacesCompositeELResolver.java:62)
        at com.sun.el.parser.AstIdentifier.getValue(AstIdentifier.java:65)
        at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:192)
        at com.sun.faces.application.ValueBindingValueExpressionAdapter.getValue(ValueBindingValueExpressionAdapter.java:102)
        at com.sun.rave.web.ui.appbase.faces.ViewHandlerImpl.pageBean(ViewHandlerImpl.java:666)
        at com.sun.rave.web.ui.appbase.faces.ViewHandlerImpl.pageBean(ViewHandlerImpl.java:641)
        at com.sun.rave.web.ui.appbase.faces.ViewHandlerImpl.renderView(ViewHandlerImpl.java:249)
        ... 36 more
}