void addConfigElement(String type, Map<String, String> props, Map<String, Map<String, String>> attributes) {
      if (props == null) {
        props = Collections.emptyMap();
      }

      if (attributes == null) {
        attributes = Collections.emptyMap();
      }
      configElements.add(new BlueprintServiceConfigElement(type, props, attributes));
    }
Internal class meant to represent the collection of configuration
items and configuration attributes that are associated with a given service.

This class is used to support proper configuration versioning when
Ambari Blueprints is used to deploy a cluster.
ambari-server/src/main/java/org/apache/ambari/server/topology/ClusterConfigurationRequest.java