title: Wicket hidden field in form: exception when injecting values
body: <p>in wicket forms get a hidden field. I found on the web, that this hidden field is needed for some kind of event handling. (Anyone knows more details?)</p>
  
  <p>I played around with XSS-Me (<a href="https://addons.mozilla.org/de/firefox/addon/7598/" rel="nofollow noreferrer">https://addons.mozilla.org/de/firefox/addon/7598/</a>) a firefox plugin, that tries to find XSS vulnerabilities.
  What the addon does, is that it injects some values into that hidden field, and then wicket throws :
     WicketRuntimeException: Attempt to access unknown request listener interface null</p>
  
  <p>Has anyone an idea, how this exception could be prevented? or caught?</p>
  
  <p>mfg bernhard</p>
  
  <p>the full trace is:</p>
  
  <pre><code>ERROR - RequestCycle               - Attempt to access unknown request listener interface null
  org.apache.wicket.WicketRuntimeException: Attempt to access unknown request listener interface null
     at org.apache.wicket.markup.html.form.Form.dispatchEvent(Form.java:1327)
     at org.apache.wicket.markup.html.form.Form.onFormSubmitted(Form.java:874)
     at sun.reflect.GeneratedMethodAccessor41.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:597)
     at org.apache.wicket.RequestListenerInterface.invoke(RequestListenerInterface.java:182)
     at org.apache.wicket.request.target.component.listener.ListenerInterfaceRequestTarget.processEvents(ListenerInterfaceRequestTarget.java:73)
     at org.apache.wicket.request.AbstractRequestCycleProcessor.processEvents(AbstractRequestCycleProcessor.java:92)
     at org.apache.wicket.RequestCycle.processEventsAndRespond(RequestCycle.java:1250)
     at org.apache.wicket.RequestCycle.step(RequestCycle.java:1329)
     at org.apache.wicket.RequestCycle.steps(RequestCycle.java:1428)
     at org.apache.wicket.RequestCycle.request(RequestCycle.java:545)
     at org.apache.wicket.protocol.http.WicketFilter.doGet(WicketFilter.java:479)
     at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:312)
     at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1089)
     at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:365)
     at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
     at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181)
     at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:712)
     at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405)
     at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:139)
     at org.mortbay.jetty.Server.handle(Server.java:295)
     at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:503)
     at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:841)
     at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:639)
     at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:210)
     at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:379)
     at org.mortbay.jetty.bio.SocketConnector$Connection.run(SocketConnector.java:226)
     at org.mortbay.thread.BoundedThreadPool$PoolThread.run(BoundedThreadPool.java:442) 
  </code></pre>