急救！！！STRUTS中提交FORM时，产生一个这样的错误：Request cannot be null

请问这是一个什么错误，问题出在什么地方。是不是配置没有做好还是别的问题？
struts-config.xml
<form-bean name="addForm" type="net.java.guestbook.form.AddForm">
<form-property name="content" type="java.lang.String" />
<form-property name="homepage" type="java.lang.String" />
<form-property name="username" type="java.lang.String" />
<form-property name="email" type="java.lang.String" />
<form-property name="oicq" type="java.lang.String" />
<form-property name="face" type="java.lang.String" />
</form-bean>

<action attribute="addForm" input="/add.jsp" name="addForm" path="/add" type="net.java.guestbook.action.AddAction">
<forward name="addok" path="/add.jsp" redirect="true" />
</action>

错误提示：
java.lang.IllegalArgumentException: Request cannot be null
at javax.servlet.ServletRequestWrapper.<init>(ServletRequestWrapper.java:50)
at javax.servlet.http.HttpServletRequestWrapper.<init>(HttpServletRequestWrapper.java:42)
at com.caucho.server.connection.RequestAdapter.<init>(RequestAdapter.java:91)
at com.caucho.server.webapp.DispatchRequest.<init>(DispatchRequest.java:67)
at com.caucho.server.webapp.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:161)
at com.caucho.server.webapp.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:121)
at com.caucho.server.webapp.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:98)
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
at org.apache.struts.action.RequestProcessor.internalModuleRelativeForward(RequestProcessor.java:1012)
at org.apache.struts.action.RequestProcessor.processValidate(RequestProcessor.java:980)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:255)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:105)
at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:149)
at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:221)
at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:257)
at com.caucho.server.port.WorkerThread.run(WorkerThread.java:123)
at java.lang.Thread.run(Thread.java:534)