Glassfish error: Response Error during finishResponse java.lang.NullPointerException
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I have Ubuntu server (8 cores, 8 gb ram) running Glassfish 3 . On GF is deployed .war app which generates static files(JSON for my Android app) into "/docroot" folder. Problem is that today strange error appeared in my logs(see below [1]). But problem is that when i checked  nagios it shows (see below [2]) that my http service was unavailable for pretty decent time today(Android app didnt worked - updated). Thats not good. My .war is running without any errors. So i dont know know where can be bug. Can it be produced by traffic? Android app updates each 15 seconds. But today i had same traffic as other days. I think server is strong and also is housed in good company.I really don't know what is origin of this behaviour. Please help.
Thank you
     
[1]

    [#|2012-07-14T15:34:59.603+0200|SEVERE|glassfish3.1.1|org.apache.catalina.connector.CoyoteAdapter|_ThreadID=23;_ThreadName=Thread-2;|PWC3989: An exception or error occurred in the container during the request processing
    java.lang.NullPointerException
	at java.lang.String.startsWith(String.java:1421)
	at java.lang.String.startsWith(String.java:1450)
	at org.apache.naming.resources.FileDirContext.file(FileDirContext.java:918)
	at org.apache.naming.resources.FileDirContext.file(FileDirContext.java:879)
	at org.apache.naming.resources.FileDirContext.lookup(FileDirContext.java:290)
	at org.apache.naming.resources.ProxyDirContext.lookup(ProxyDirContext.java:334)
	at com.sun.grizzly.util.http.mapper.Mapper.internalMapWrapper(Mapper.java:1213)
	at com.sun.grizzly.util.http.mapper.Mapper.internalMap(Mapper.java:961)
	at com.sun.grizzly.util.http.mapper.Mapper.map(Mapper.java:820)
	at org.apache.catalina.connector.CoyoteAdapter.postParseRequest(CoyoteAdapter.java:507)
	at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:271)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
	at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
	at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
	at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
	at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
	at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
	at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
	at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
	at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
	at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
	at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	at java.lang.Thread.run(Thread.java:619)
[2]
  http://i45.tinypic.com/29nf9c7.png