code: protected List<Metric> mapping(List<Metric> metrics, List<String> constants) {
  		SystemAssert.requireArgument(metrics != null, "Cannot transform null metrics");
  
  		if (metrics.isEmpty()) {
  			return metrics;
  		}
  
  		List<Metric> newMetricsList = new ArrayList<Metric>();
  
  		for (Metric metric : metrics) {
  			metric.setDatapoints(this.valueReducerOrMapping.mapping(metric.getDatapoints(), constants));
  			newMetricsList.add(metric);
  		}
  		return newMetricsList;
  	}
docs: Mapping a list of metric, only massage its datapoints.
  
  @param   metrics    The list of metrics to be mapped. constants The list of constants used for mapping
  @param   constants  constants input
  
  @return  A list of metrics after mapping.