我画了报表，只要一拖入值，预览就错，可是我预览数据集是存在值的，我想知道是为什么会报这个错

java.lang.NullPointerException
	at com.fr.data.index.AbstractIndexDataModel.getColumnCount(Unknown Source)
	at com.fr.report.core.A.J.dealWithBEDSColumn(Unknown Source)
	at com.fr.report.core.A.m.cc_ce_array(Unknown Source)
	at com.fr.report.core.A.J.A(Unknown Source)
	at com.fr.report.core.A.J.A(Unknown Source)
	at com.fr.report.core.A.J.A(Unknown Source)
	at com.fr.report.core.A.J.A(Unknown Source)
	at com.fr.report.core.A.J.A(Unknown Source)
	at com.fr.report.core.A.J.C(Unknown Source)
	at com.fr.report.core.A.J.execute4Expand(Unknown Source)
	at com.fr.report.core.A.J.execute(Unknown Source)
	at com.fr.report.worksheet.WorkSheet.execute(Unknown Source)
	at com.fr.report.core.sheet.AbstractWorkBookExecutor._execute(Unknown Source)
	at com.fr.report.core.sheet.AbstractWorkBookExecutor.execute(Unknown Source)
	at com.fr.main.impl.WorkBook.execute(Unknown Source)
	at com.fr.main.impl.WorkBook.execute(Unknown Source)
	at com.fr.web.cache.ReportCache.getResultWorkBook(Unknown Source)
	at com.fr.stable.PageActor.getResultBookFromCacheIfNeed(Unknown Source)
	at com.fr.main.impl.WorkBookTemplateDelegate.execute(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.execute(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.computeBook2Show$original$YE8QNKn3(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.computeBook2Show$original$YE8QNKn3$accessor$DsGVt2KA(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor$auxiliary$OQttfOv3.call(Unknown Source)
	at com.fr.intelli.metrics.MonitorInterceptor.intercept(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.computeBook2Show(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.initBook2Show(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.getWorkBook2Show(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.getWorkBook2Show(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.getResultWorkBook(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.createPageSetChain(Unknown Source)
	at com.fr.web.core.ReportSessionIDInfor.getReportPage(Unknown Source)
	at com.fr.web.core.B.qA.A(Unknown Source)
	at com.fr.web.core.B.qA.A(Unknown Source)
	at com.fr.web.core.B.kA.A(Unknown Source)
	at com.fr.web.core.B.KA.actionCMD(Unknown Source)
	at com.fr.web.core.WebActionsDispatcher.dealForActionCMD(Unknown Source)
	at com.fr.web.core.WebActionsDispatcher.dealForActionDefaultCmd(Unknown Source)
	at com.fr.web.core.B.hA.process(Unknown Source)
	at com.fr.web.core.ReportDispatcher.dealWithOp(Unknown Source)
	at com.fr.web.core.ReportDispatcher.dealWeblet(Unknown Source)
	at com.fr.web.core.ReportDispatcher.dealWithRequest(Unknown Source)
	at com.fr.web.controller.BaseRequestService.preview(Unknown Source)
	at com.fr.web.controller.ReportRequestService.preview(Unknown Source)
	at sun.reflect.GeneratedMethodAccessor95.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.fr.third.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
	at com.fr.third.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137)
	at com.fr.third.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
	at com.fr.third.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:747)
	at com.fr.third.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:676)
	at com.fr.third.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
	at com.fr.third.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:938)
	at com.fr.third.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:870)
	at com.fr.third.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:961)
	at com.fr.third.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	at com.fr.third.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.fr.third.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at com.fr.third.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.fr.decision.base.DecisionServletInitializer$4.doFilter(Unknown Source)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)