jdonFramework里面train实例报错，请帮帮忙

严重: Servlet.service() for servlet action threw exception
javax.servlet.ServletException: getPageIterator's result is null, check your ModelListAction subclass
at org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:516)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:423)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:226)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1164)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:397)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:743)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:286)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at com.jdon.util.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:92)
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:256)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:562)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:974)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:205)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:562)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:974)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:177)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:562)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:974)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:156)
at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:562)
at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:974)
at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:203)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:637)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:484)
at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:568)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:631)
at java.lang.Thread.run(Thread.java:534)