*         .collect(
   *             flatteningToImmutableSetMultimap(
   *                  str -> str.charAt(0),
   *                  str -> str.substring(1).chars().mapToObj(c -> (char) c));
   *
   * // is equivalent to
   *
   * static final ImmutableSetMultimap<Character, Character> FIRST_LETTER_MULTIMAP =
   *     ImmutableSetMultimap.<Character, Character>builder()

   *         .collect(
   *             flatteningToImmutableListMultimap(
   *                  str -> str.charAt(0),
   *                  str -> str.substring(1).chars().mapToObj(c -> (char) c));
   *
   * // is equivalent to
   *
   * static final ImmutableListMultimap<Character, Character> FIRST_LETTER_MULTIMAP =
   *     ImmutableListMultimap.<Character, Character>builder()

    private static final String ILLEGAL_FS_CHARS = "\\/:\"<>|?*";

    private static final String ILLEGAL_VERSION_CHARS = ILLEGAL_FS_CHARS;

    private static final String ILLEGAL_REPO_ID_CHARS = ILLEGAL_FS_CHARS;

    private static final String EMPTY = "";

   *     Stream.of("banana", "apple", "carrot", "asparagus", "cherry")
   *         .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;