code: public static <T> Range<T> is(final T element, final Comparator<T> comparator) {
          return between(element, element, comparator);
      }
docs: <p>Obtains a range using the specified element as both the minimum
  and maximum in this range.</p>
  
  <p>The range uses the specified {@code Comparator} to determine where
  values lie in the range.</p>
  
  @param <T> the type of the elements in this range
  @param element  the value to use for this range, must not be {@code null}
  @param comparator  the comparator to be used, null for natural ordering
  @return the range object, not null
  @throws IllegalArgumentException if the element is null
  @throws ClassCastException if using natural ordering and the elements are not {@code Comparable}