ServletWebResponse/RequestCycle: NPE after upgrading from 6.0.0 to 6.2.0

My WebAplication uses the following code to get rid of the jsessionid parameter for certain user agents, which worked fine with Wicket 6.0.0 but results in a NullPointerException now.

@Override
protected WebResponse newWebResponse(final WebRequest webRequest, final HttpServletResponse httpServletResponse){
return new ServletWebResponse((ServletWebRequest)webRequest, httpServletResponse) {

@Override
public String encodeURL(CharSequence url)

{ final String agent = webRequest.getHeader("User-Agent"); return isAgent(agent) ? url.toString() : super.encodeURL(url); }

@Override
public String encodeRedirectURL(CharSequence url)

{ return encodeURL(url); }

};
}

It is exactly the same issue as discussed here (about version 6.1.1):
http://comments.gmane.org/gmane.comp.java.wicket.user/106013

ServletWebResponse:181 - RequestCycle.get() returns null.

Workaround is to check for null before calling super.encodeURL(url), but I assume this is a bug?