code: public String toHexString() {
      final StringBuilder buf = new StringBuilder(24);
  
      for (final byte b : toByteArray()) {
        buf.append(String.format("%02x", b & 0xff));
      }
  
      return buf.toString();
    }
docs: Converts this instance into a 24-byte hexadecimal string representation.
  
  @return a string representation of the ObjectId in hexadecimal format