@JsonIgnore
    public Map<String, Set<String>> getHostgroupHostMap() {
      return hostGroups.stream().collect(toMap(BindingHostGroup::getName, BindingHostGroup::getHostNames));
    }
@return value attributes in <i>attribute name -> property name -> value</i> format
ambari-server/src/main/java/org/apache/ambari/server/api/services/stackadvisor/recommendations/RecommendationResponse.java