@Override
    public Iterator<T> iterator() {
        return set.iterator();
    }
By default the criteria will match anything. NULL matchAll implies match
anything when nothing is in the set or we are to not matchNull. By
setting match all it will match all regardless.
stroom-legacy/stroom-legacy-model_6_1/src/main/java/stroom/legacy/model_6_1/CriteriaSet.java