String[] spaces = (String[]) propMap.get(CRAWLER_DOCUMENT_SPACES);
        if (spaces == null) {
            spaces = Arrays.stream(getCrawlerDocumentSpaceCharsAsArray()).mapToObj(Character::toString).toArray(n -> new String[n]);
            propMap.put(CRAWLER_DOCUMENT_SPACES, spaces);
        }
        return spaces;
    }

   *         .collect(
   *             flatteningToMultimap(
   *                  str -> str.charAt(0),
   *                  str -> str.substring(1).chars().mapToObj(c -> (char) c),
   *                  MultimapBuilder.linkedHashKeys().arrayListValues()::build));
   *
   * // is equivalent to
   *
   * static final ListMultimap<Character, Character> FIRST_LETTER_MULTIMAP;
   *