code: private List<Metric> mapping(List<Metric> metrics) {
          SystemAssert.requireArgument(metrics != null, "Cannot transform empty metric/metrics");
          if (metrics.isEmpty()) {
              return metrics;
          }
  
          List<Metric> newMetricsList = new ArrayList<Metric>();
  
          for (Metric metric : metrics) {
              Map<Long, Double> cleanDatapoints = cleanDPs(metric.getDatapoints());
  
              metric.setDatapoints(this.valueMapping.mapping(cleanDatapoints));
              newMetricsList.add(metric);
          }
          return newMetricsList;
      }
docs: Mapping a list of metric, only massage its datapoints.
  
  @param   metrics  The list of metrics to be mapped.
  
  @return  A list of metrics after mapping.