docs: List<MetricDatum> metricData() {
          Batch batch = new Batch();
          return getMeters().stream().flatMap(m -> m.match(
                  batch::gaugeData,
                  batch::counterData,
                  batch::timerData,
                  batch::summaryData,
                  batch::longTaskTimerData,
                  batch::timeGaugeData,
                  batch::functionCounterData,
                  batch::functionTimerData,
                  batch::metricData)
          ).collect(toList());
      }