code: @Override
      public void transform(Context<MutableTimeSeriesCollectionPair> ctx) {
          DateTime now = ctx.getTSData().getCurrentCollection().getTimestamp();
  
          ctx.getTSData().getCurrentCollection().addMetrics(MONITOR_GROUP, get_metrics_(now, ctx));
  
          ctx.getAlertManager().accept(new Alert(now, MONITOR_DOWN_ALERT, () -> "builtin rule", Optional.of(false), Duration.ZERO, "builtin rule: monitor is not running for some time", EMPTY_MAP));
      }
docs: Emit an alert monitor.down, which is in the OK state.
  
  @param ctx Rule evaluation context.