private static IntObjectMap<ConjunctionIndex.FeatureIndex> buildKIndex(HashMap<Integer, FeatureIndexBuilder> kIndexBuilder) {
        IntObjectHashMap<ConjunctionIndex.FeatureIndex> map = new IntObjectHashMap<>();
        for (Map.Entry<Integer, FeatureIndexBuilder> entry : kIndexBuilder.entrySet()) {
            map.put(entry.getKey(), buildFeatureIndex(entry.getValue()));
        }
        map.compact();
        return map;
    }
@return The number of unique conjunctions indexed.
predicate-search/src/main/java/com/yahoo/search/predicate/index/conjunction/ConjunctionIndexBuilder.java