durationInNanos(that.refreshDuration, that.refreshTimeUnit));
  }

  /**
   * Converts an expiration duration/unit pair into a single Long for hashing and equality. Uses
   * nanos to match CacheBuilder implementation.
   */
  @CheckForNull
  private static Long durationInNanos(long duration, @CheckForNull TimeUnit unit) {
    return (unit == null) ? null : unit.toNanos(duration);