public static <T, U extends Comparable<? super U>> Collector<T, ?, Optional<Long>> denseRankBy(U value, Function<? super T, ? extends U> function) {
        return denseRankBy(value, function, naturalOrder());
    }
Get a {@link Collector} that calculates the derived <code>DENSE_RANK()</code> function given natural ordering.
jOOL-java-8/src/main/java/org/jooq/lambda/Agg.java