code: public String hash(String key) {
      Objects.requireNonNull(key);
      return Hashing.sha256()
          .hashString(key, StandardCharsets.UTF_8)
          .toString();
    }
docs: Generates a SHA-256 hash of a String.
  Since {@link Preferences#MAX_KEY_LENGTH} is 80, if the breadcrumb is over 80 characters, it
  will lead to an exception while saving. This method generates a SHA-256 hash of the breadcrumb
  to save / load as the key in {@link Preferences}, since those are guaranteed to be
  maximum 64 chars long.
  
  @return SHA-256 representation of breadcrumb