* write operations. Expired entries are cleaned up as part of the routine maintenance described
   * in the class javadoc.
   *
   * <p>If you can represent the duration as a {@link java.time.Duration} (which should be preferred
   * when feasible), use {@link #expireAfterWrite(Duration)} instead.
   *
   * @param duration the length of time after an entry is created that it should be automatically
   *     removed