NullPointerException on htmlunit.WebClient.getPage #310

Exception in thread "main" java.lang.RuntimeException: java.lang.RuntimeException: java.lang.NullPointerException
at com.gargoylesoftware.htmlunit.html.HtmlPage.cleanUp(HtmlPage.java:360)
at com.gargoylesoftware.htmlunit.WebClient.loadWebResponseInto(WebClient.java:592)
at com.gargoylesoftware.htmlunit.WebClient.getPage(WebClient.java:456)
at com.gargoylesoftware.htmlunit.WebClient.getPage(WebClient.java:368)
at com.gargoylesoftware.htmlunit.WebClient.getPage(WebClient.java:541)
at com.ibm.as400.pt.viewer.script.RunPDIReport.exportDispatchServlet(RunPDIReport.java:477)
at com.ibm.as400.pt.viewer.script.RunPDIReport.doLoginAndExport(RunPDIReport.java:407)
at com.ibm.as400.pt.viewer.script.RunPDIReport.main(RunPDIReport.java:178)
Caused by: java.lang.RuntimeException: java.lang.NullPointerException
at com.gargoylesoftware.htmlunit.javascript.host.WebSocket.close(WebSocket.java:408)
at com.gargoylesoftware.htmlunit.javascript.host.WebSocket.close(WebSocket.java:377)
at com.gargoylesoftware.htmlunit.html.HtmlPage.cleanUp(HtmlPage.java:357)
... 7 more
Caused by: java.lang.NullPointerException
at com.gargoylesoftware.htmlunit.websocket.JettyWebSocketAdapter.closeClinet(JettyWebSocketAdapter.java:135)
at com.gargoylesoftware.htmlunit.javascript.host.WebSocket.close(WebSocket.java:405)
... 9 more

**The dispatch request is : **

WebRequest[<url="http://localhost:9080/Navigator/DispatcherServlet/perf/loadPerspectives", POST, EncodingType[name=application/x-www-form-urlencoded], [], {Cookie=JSESSIONID=0000zGsxZkz6VSlx5FVsoC1SgaW:8f560a86-b308-4406-8092-29d0c4eb66be, Accept=/, Accept-Encoding=gzip, deflate, Content-Type=application/json}, null>]

The code is:

	URL loadPerspUrl = new URL("http://"+getSystemName()+":9080/Navigator/DispatcherServlet/perf/loadPerspectives");
	WebRequest requestSettings = new WebRequest(loadPerspUrl, HttpMethod.POST);
	requestSettings.setAdditionalHeader("Content-Type", "application/json");
	requestSettings.setAdditionalHeader("Cookie", m_cookie_jsessionid);

	Page redirectPage = webClient.getPage(requestSettings);  // line 477 **exception occurs here **
	webClient.waitForBackgroundJavaScriptStartingBefore(10000);
		
	WebResponse response = redirectPage.getWebResponse();