code: protected void redirectToReferrer(String defaultReference) {
          String referrer = context.requestHeader("Referer");
          referrer = referrer == null? defaultReference: referrer;
          redirect(referrer);
      }
docs: Redirects to referrer if one exists. If a referrer does not exist, it will be redirected to
  the <code>defaultReference</code>.
  
  @param defaultReference where to redirect - can be absolute or relative; this will be used in case
  the request does not provide a "Referrer" header.
  @return {@link HttpSupport.HttpBuilder}, to accept additional information.