code: private List<Integer> encodeInfoKeys(Collection<String> keys) {
          // sorted key list
          List<Integer> idxKeys = new ArrayList<>(keys.size());
          for (String key : keys) {
              if (!IGNORED_ATTRIBUTE_KEYS.contains(key) && (includeAllFormats || attributeFields.contains(key))) {
                  Integer idx = infoKeyIndexMap.get(key);
                  if (idx != null) {
                      idxKeys.add(idx);
                  } else {
                      throw new IllegalArgumentException("Unknown key value " + key);
                  }
              }
          }
          idxKeys.sort(Integer::compareTo);
          return idxKeys;
      }
docs: Creates a sorted list of strings from the INFO KEYs
  
  @return {@link List}
  @param keys