public static <T> Comparator<T> nonNull(final Comparator<T> comparator) {
        return NullSafe.requireNonNullElseGet(comparator, CompareUtil::noOpComparator);
    }
Returns a non-null comparator, either comparator if non-null, else a no-op
comparator ({@link CompareUtil#noOpComparator()}) that does nothing.
stroom-util-shared/src/main/java/stroom/util/shared/CompareUtil.java