public void incMetric(String name,int increment) {
        Integer currentValue=metrics.get(name);
        if (currentValue==null)
            currentValue=0;
        metrics.put(name,currentValue+increment);
    }
Increases the metric by the given name by increment, if the metric is not previously set,
this will assign it the value increment as expected
searchlib/src/main/java/com/yahoo/searchlib/rankingexpression/evaluation/OptimizationReport.java