private Double getMetric(String name, Map<String, ?> dimensions) {
        Map<Map<String, ?>, Double> metric = metrics.metrics().get(name);
        if (metric == null) throw new IllegalArgumentException("Metric '" + name + "' not found");
        return metric.get(dimensions);
    }
@author Morten Tokle
@author Martin Polden
routing-generator/src/test/java/com/yahoo/vespa/hosted/routing/nginx/NginxMetricsReporterTest.java