code: public static Set<String> getSet(AbstractConfig config, String key) {
      List<String> value = config.getList(key);
      return ImmutableSet.copyOf(value);
    }
docs: Method is used to retrieve a list and convert it to an immutable set.
  
  @param config Config to read
  @param key    Key to read
  @return ImmutableSet with the contents of the config key.
  @see com.google.common.collect.ImmutableSet