code: @SuppressWarnings("unchecked")
    public static List<String> readStringListFromConfAsJson(String key, Configuration conf) {
      String json = conf.get(key);
      if (json == null) {
        return null;
      }
      return Lists.<String>newArrayList(((JSONArray) JSONValue.parse(json)));
    }
docs: Reads a list of strings stored as a json array from  a configuration
  
  @param key for the configuration
  @param conf to read from
  @return the read list of strings, or null if key is not present in conf