code: private void checkHeartbeatTimeout(PropertyKey intervalKey, PropertyKey timeoutKey) {
      long interval = getMs(intervalKey);
      long timeout = getMs(timeoutKey);
      Preconditions.checkState(interval < timeout,
          "heartbeat interval (%s=%s) must be less than heartbeat timeout (%s=%s)", intervalKey,
          interval, timeoutKey, timeout);
    }
docs: Checks that the interval is shorter than the timeout.
  
  @param intervalKey property key for an interval
  @param timeoutKey property key for a timeout