public Set<ReferenceNode> getRankFeatures() {
        if (rankFeatures != null) return Collections.unmodifiableSet(rankFeatures);
        return uniquelyInherited(RankProfile::getRankFeatures, f -> ! f.isEmpty(), "summary-features")
                .orElse(Set.of());
    }
Returns a read-only view of the rank features to use in this profile. This is never null
config-model/src/main/java/com/yahoo/schema/RankProfile.java