this.refreshNanos = unit.toNanos(duration);
    return this;
  }

  @SuppressWarnings("GoodTime") // nanos internally, should be Duration
  long getRefreshNanos() {
    return (refreshNanos == UNSET_INT) ? DEFAULT_REFRESH_NANOS : refreshNanos;
  }

  /**
   * Specifies a nanosecond-precision time source for this cache. By default, {@link
   * System#nanoTime} is used.