code: public static BackoffStrategy randomBackoff(long maximumTime, TimeUnit timeUnit) {
          Preconditions.checkNotNull(timeUnit, "The time unit may not be null");
          return new RandomBackoffStrategy(0L, timeUnit.toMillis(maximumTime));
      }
docs: Returns a strategy that waits a random amount of time before retrying.
  
  @param maximumTime the maximum time to wait
  @param timeUnit    the unit of the maximum time
  @return a backoff strategy with a random wait time
  @throws IllegalStateException if the maximum wait time is &lt;= 0.