cas client 3.1.1 and simple WebApp sample

[Laura QCaballero]

Hi, 
  Maybe this is a stupid question...
  I'm following the steps as this page explains: http://www.ja-sig.org/wiki/display/CASC/JA-SIG+Java+Client+Simple+WebApp+Sample, but I'm doing it on two different machines, both on Ubuntu. My first machine is the Cas Server and the other one has the mywebapp.war. Each one having a Tomcat Server.

I get the following exception:

java.lang.NullPointerException
	at org.jasig.cas.client.util.HttpServletRequestWrapperFilter$CasHttpServletRequestWrapper.getRemoteUser(HttpServletRequestWrapperFilter.java:80)
	at org.apache.jsp.include_005fheader_jsp._jspService(include_005fheader_jsp.java:46)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
	at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:691)
	at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:594)
	at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:505)
        (...)

And I'm trying to apply the patch mentioned in the page, but I don't know exactly where to do it. Inside mywebapp there isn't any  HttpServletRequestWrapperFilter.java
There is a HttpServletRequestWrapperFilter.java in cas-client-3.1.1 I downloaded, but I have used it just to get the necessary jars added to mywebapp.war. 

Sorry if this is very stupid. 
Any help would be very appreciated
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