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