Intermittently i receive the following error while executing the portlet developed using icefaces 1.8.2. Can you pl help resolve this issue?

14:20:11,082 ERROR [[Blocking Servlet]] Servlet.service() for servlet Blocking Servlet threw exception
java.lang.RuntimeException: wrapped Exception: java.lang.NullPointerException
        at com.icesoft.faces.webapp.http.servlet.MainServlet.service(MainServlet.java:156)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at com.icesoft.faces.webapp.xmlhttp.BlockingServlet.service(BlockingServlet.java:56)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        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:235)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
        at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:190)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:433)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:92)
        at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.process(SecurityContextEstablishmentValve.java:126)
        at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:70)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:330)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:829)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:598)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NullPointerException
        at org.apache.tomcat.util.http.MimeHeaders.setValue(MimeHeaders.java:382)
        at org.apache.coyote.Response.setHeader(Response.java:337)
        at org.apache.catalina.connector.Response.setHeader(Response.java:1396)
        at org.apache.catalina.connector.ResponseFacade.setHeader(ResponseFacade.java:480)
        at com.icesoft.faces.webapp.http.servlet.ServletRequestResponse.setHeader(ServletRequestResponse.java:217)
        at com.icesoft.faces.webapp.http.common.standard.FixedXMLContentHandler.respond(FixedXMLContentHandler.java:13)
        at com.icesoft.faces.webapp.http.servlet.ServletRequestResponse.respondWith(ServletRequestResponse.java:201)
        at com.icesoft.faces.webapp.http.core.SendUpdates.service(SendUpdates.java:36)
        at com.icesoft.faces.webapp.http.core.RequestVerifier.service(RequestVerifier.java:31)
        at com.icesoft.faces.webapp.http.common.standard.PathDispatcherServer.service(PathDispatcherServer.java:24)
        at com.icesoft.faces.webapp.http.servlet.BasicAdaptingServlet.service(BasicAdaptingServlet.java:16)
        at com.icesoft.faces.webapp.http.servlet.PathDispatcher.service(PathDispatcher.java:23)
        at com.icesoft.faces.webapp.http.servlet.SessionDispatcher.service(SessionDispatcher.java:53)
        at com.icesoft.faces.webapp.http.servlet.SessionVerifier.service(SessionVerifier.java:26)
        at com.icesoft.faces.webapp.http.servlet.PathDispatcher.service(PathDispatcher.java:23)
        at com.icesoft.faces.webapp.http.servlet.MainServlet.service(MainServlet.java:131)
        ... 23 more