@Inject
  public static void init(Injector injector) {
    clusters = injector.getInstance(Clusters.class);
    metaInfo = injector.getInstance(AmbariMetaInfo.class);
    metricPropertyProviderFactory = injector.getInstance(MetricPropertyProviderFactory.class);
    StackDefinedPropertyProvider.injector = injector;
  }
PropertyHelper/AbstractPropertyProvider expect map of maps,
that's why we wrap metrics into map
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/StackDefinedPropertyProvider.java