} else if (accum == Long.MIN_VALUE) {
      return null;
    } else {
      return -accum;
    }
  }

  private static final class LongConverter extends Converter<String, Long> implements Serializable {
    static final Converter<String, Long> INSTANCE = new LongConverter();

    @Override
    protected Long doForward(String value) {
      return Long.decode(value);
    }

    @Override