> 我今天下了北京大学的acm的测试系统，测试时出现了这样的错误。有谁知道是为什么吗????
> Exception Occurred
> 
>   
> Exception stack 
> java.lang.NullPointerException
> 	at com.pku.judgeonline.common.FormattedOut.printHead(Unknown Source)
> 	at com.pku.judgeonline.servlet.Index.doGet(Unknown Source)
> 	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:284)
> 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:204)
> 	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:564)
> 	at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:245)
> 	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:199)
> 	at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
> 	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:564)
> 	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:195)
> 	at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:151)
> 	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:164)
> 	at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:149)
> 	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:564)
> 	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:564)
> 	at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:972)
> 	at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:211)
> 	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:805)
> 	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:696)
> 	at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:605)
> 	at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:677)
> 	at java.lang.Thread.run(Unknown Source)
> 
> 谁知道能不能看解决办法发到我邮箱:cqqpp@126.com,非常感谢!