public void addFeatureNormalizer(RankFeatureNormalizer n) {
        if (functions.get(n.name()) != null) {
            throw new IllegalArgumentException("cannot use name '" + name + "' for both function and normalizer");
        }
        featureNormalizers.add(n);
    }
Returns the path type, if valuePath is set.
config-model/src/main/java/com/yahoo/schema/RankProfile.java