docs: private static String popParam(final Map<String, List<String>> querystring,
                                       final String param) {
      final List<String> params = querystring.remove(param);
      if (params == null) {
        return null;
      }
      final String given = params.get(params.size() - 1);
      // TODO - far from perfect, should help a little.
      if (given.contains("`") || given.contains("%60") || 
          given.contains("&#96;")) {
        throw new BadRequestException("Parameter " + param + " contained a "
            + "back-tick. That's a no-no.");
      }
      return given;
    }