code: @Nullable
    public static String getRequestQueryString (@Nullable final HttpServletRequest aRequest)
    {
      String ret = null;
      if (aRequest != null)
        try
        {
          if (aRequest.isAsyncSupported () && aRequest.isAsyncStarted ())
            ret = (String) aRequest.getAttribute (AsyncContext.ASYNC_QUERY_STRING);
          else
            ret = aRequest.getQueryString ();
        }
        catch (final Exception ex)
        {
          // fall through
          if (isLogExceptions ())
            if (LOGGER.isWarnEnabled ())
              LOGGER.warn ("[ServletHelper] Failed to determine query string of HTTP request", ex);
        }
      return ret;
    }
docs: Work around an exception that can occur in Jetty 9.3.13:
  
  <pre>
  java.lang.NullPointerException: null
  at org.eclipse.jetty.server.Request.getQueryString(Request.java:1119) ~[jetty-server-9.3.13.v20161014.jar:9.3.13.v20161014]
  at com.helger.web.servlet.request.RequestHelper.getURL(RequestHelper.java:340) ~[ph-web-8.6.2.jar:8.6.2]
  </pre>
  
  @param aRequest
  Source request. May be <code>null</code>.
  @return <code>null</code> if request is <code>null</code> or if no query
  string could be determined, or if none is present