code: public static void addAdditionalNamenodesToProps(Props props, String additionalNamenodes) {
      String otherNamenodes = props.get(OTHER_NAMENODES_PROPERTY);
      if (otherNamenodes != null && otherNamenodes.length() > 0) {
        props.put(OTHER_NAMENODES_PROPERTY, otherNamenodes + "," + additionalNamenodes);
      } else {
        props.put(OTHER_NAMENODES_PROPERTY, additionalNamenodes);
      }
    }
docs: Takes the list of other Namenodes from which to fetch delegation tokens,
  the {@link #OTHER_NAMENODES_PROPERTY} property, from Props and inserts it
  back with the addition of the the potentially JobType-specific Namenode URIs
  from additionalNamenodes. Modifies props in-place.
  
  @param props Props to add the new Namenode URIs to.
  @param additionalNamenodes Comma-separated list of Namenode URIs from which to fetch
  delegation tokens.