code: public String getParameterNameAt(int index) {
      if (info == null || info.parameters == null) {
        return null;
      }
      if (index >= info.parameters.size()) {
        return null;
      }
      return Iterables.get(info.parameters.keySet(), index);
    }
docs: Returns the nth name in the defined parameters. The iteration order
  is the order in which parameters are defined in the JSDoc, rather
  than the order in which the function declares them.