private static ContainerCluster<?> getContainerWithSearch(Collection<ContainerModel> containers) {
        for (ContainerModel container : containers)
            if (container.getCluster().getSearch() != null)
                return container.getCluster();
        return null;
    }
Returns indexing cluster implicitly created by this,
or empty if an explicit cluster is used (or if called before the build phase)
config-model/src/main/java/com/yahoo/vespa/model/content/Content.java