code: public static Identifier fromUuid(UUID uuid) {
          ByteBuffer buf = ByteBuffer.allocate(16);
          buf.putLong(uuid.getMostSignificantBits());
          buf.putLong(uuid.getLeastSignificantBits());
          return new Identifier(buf.array());
      }
docs: Transforms a {@link java.util.UUID} into an Identifier.
  No mangling with strings, only the underlying bytes of the
  UUID are used so this is fast and stable.