code: public static void checkMinimalPollingPeriod(TimeUnit pollUnit, int pollPeriod)
        throws IllegalArgumentException {
      int period = (int) MINIMAL_POLL_UNIT.convert(pollPeriod, pollUnit);
      Preconditions.checkArgument(period >= MINIMAL_POLL_PERIOD,
          "Polling period %d %d is below the minimal polling period", pollPeriod, pollUnit);
    }
docs: Checks if the poll period is smaller that the minimal poll period which is 1 second.
  
  @param pollUnit the polling unit
  @param pollPeriod the polling period
  @throws IllegalArgumentException if the polling period is invalid