}
    if (refresh != null) {
      builder.refreshAfterWrite(refresh.duration, refresh.unit);
    }
    if (keyStrength != null) {
      builder.setKeyStrength(keyStrength);
    }
    if (valueStrength != null) {
      builder.setValueStrength(valueStrength);
    }
    return builder;
  }

  static class DurationSpec {
    private final long duration;