FreeMarker template error!

Expression Session.auth is undefined on line 10, column 22 in nutz/admin/index.ftl. The problematic instruction: ---------- ==> if-else [on line 10, column 17 in nutz/admin/index.ftl] ---------- Java backtrace for programmers: ---------- freemarker.core.InvalidReferenceException: Expression Session.auth is undefined on line 10, column 22 in nutz/admin/index.ftl. 	at freemarker.core.TemplateObject.assertNonNull(TemplateObject.java:124) 	at freemarker.core.TemplateObject.invalidTypeException(TemplateObject.java:134) 	at freemarker.core.Dot._getAsTemplateModel(Dot.java:78) 	at freemarker.core.Expression.getAsTemplateModel(Expression.java:89) 	at freemarker.core.Dot._getAsTemplateModel(Dot.java:74) 	at freemarker.core.Expression.getAsTemplateModel(Expression.java:89) 	at freemarker.core.Expression.isTrue(Expression.java:138) 	at freemarker.core.IfBlock.accept(IfBlock.java:80) 	at freemarker.core.Environment.visit(Environment.java:210) 	at freemarker.core.MixedContent.accept(MixedContent.java:92) 	at freemarker.core.Environment.visit(Environment.java:210) 	at freemarker.core.Environment.process(Environment.java:190) 	at freemarker.template.Template.process(Template.java:237) 	at org.nutz.mvc.view.freemarker.FreemarkerView.render(FreemarkerView.java:92) 	at org.nutz.mvc.impl.processor.ViewProcessor.process(ViewProcessor.java:39) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.MethodInvokeProcessor.process(MethodInvokeProcessor.java:24) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.AdaptorProcessor.process(AdaptorProcessor.java:33) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.ActionFiltersProcessor.process(ActionFiltersProcessor.java:40) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.ModuleProcessor.process(ModuleProcessor.java:99) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.EncodingProcessor.process(EncodingProcessor.java:27) 	at org.nutz.mvc.impl.processor.AbstractProcessor.doNext(AbstractProcessor.java:44) 	at org.nutz.mvc.impl.processor.UpdateRequestAttributesProcessor.process(UpdateRequestAttributesProcessor.java:15) 	at org.nutz.mvc.impl.NutActionChain.doChain(NutActionChain.java:40) 	at org.nutz.mvc.impl.ActionInvoker.invoke(ActionInvoker.java:64) 	at org.nutz.mvc.ActionHandler.handle(ActionHandler.java:31) 	at org.nutz.mvc.NutFilter.doFilter(NutFilter.java:94) 	at org.nutz.mvc.HaoFilter.doFilter(HaoFilter.java:41) 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243) 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) 	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) 	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) 	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171) 	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) 	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936) 	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) 	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) 	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004) 	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) 	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) 	at java.lang.Thread.run(Thread.java:744)