@Override
    public int hashCode() {
        final HashCodeBuilder hashCodeBuilder = new HashCodeBuilder();
        hashCodeBuilder.append(set);
        hashCodeBuilder.append(matchAll);
        hashCodeBuilder.append(matchNull);
        return hashCodeBuilder.toHashCode();
    }
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