private boolean likelyHitsHaveCorrectValueForSortFields() {
        if (hitOrderer == null) {
            return true;
        } else {
            Set<String> filledFields = getFilled();
            return filledFields == null || !filledFields.isEmpty();
        }
    }
Force hit sorting now.
This is not normally useful because a group will stay sorted automatically,
but it is in the case where
the hits have changed their internal state in a way that should change ordering
container-search/src/main/java/com/yahoo/search/result/HitGroup.java