code: public static <T extends Comparable<? super T>> TopKSelector<T> least(int k) {
      return least(k, Ordering.natural());
    }
docs: Returns a {@code TopKSelector} that collects the lowest {@code k} elements added to it,
  relative to the natural ordering of the elements, and returns them via {@link #topK} in
  ascending order.
  
  @throws IllegalArgumentException if {@code k < 0}