private SourceGroup getGroup(ComponentId sourceId) {
        ComponentAdaptor<SourceGroup> group =
                sourceGroups.getComponent(sourceId);
        if (group == null) {
            group = new ComponentAdaptor<>(sourceId,
                    new SourceGroup(sourceId));
            sourceGroups.register(group.getId(), group);
        }
        return group.model;
    }
Owns all the source groups in the search chains model.
@author Tony Vaagenes
config-model/src/main/java/com/yahoo/vespa/model/container/search/searchchain/SourceGroupRegistry.java