code: @Nullable
      public Long getMaxStaleness(final TimeUnit timeUnit) {
          notNull("timeUnit", timeUnit);
          if (maxStalenessMS == null) {
              return null;
          }
          return timeUnit.convert(maxStalenessMS, TimeUnit.MILLISECONDS);
      }
docs: Gets the maximum acceptable staleness of a secondary in order to be considered for read operations.
  <p>
  The maximum staleness feature is designed to prevent badly-lagging servers from being selected. The staleness estimate is imprecise
  and shouldn't be used to try to select "up-to-date" secondaries.
  </p>
  <p>
  The driver estimates the staleness of each secondary, based on lastWriteDate values provided in server isMaster responses,
  and selects only those secondaries whose staleness is less than or equal to maxStaleness.
  </p>
  @param timeUnit the time unit in which to return the value
  @return the maximum acceptable staleness in the given time unit, or null if the value is not set
  @mongodb.server.release 3.4
  @since 3.4