code: public Set<String> getParameterNames() {
      if (info == null || info.parameters == null) {
        return ImmutableSet.of();
      }
      return ImmutableSet.copyOf(info.parameters.keySet());
    }
docs: Returns the set of names of the defined parameters. The iteration order
  of the returned set is the order in which parameters are defined in the
  JSDoc, rather than the order in which the function declares them.
  
  @return the set of names of the defined parameters. The returned set is
  immutable.