public void merge(AutoBalancerMetrics metric) {
            String mergeKey = metric.key();
            AutoBalancerMetrics prev = metricMap.putIfAbsent(mergeKey, metric);
            if (prev != null) {
                prev.add(metric);
            }
        }
This class was modified based on Cruise Control: com.linkedin.kafka.cruisecontrol.metricsreporter.metric.YammerMetricProcessor.
core/src/main/java/kafka/autobalancer/metricsreporter/metric/YammerMetricProcessor.java