Returns the greatest element in this set strictly less than the
given element, or {@code null} if there is no such element.
@param e the value to match
@return the greatest element less than {@code e},
or {@code null} if there is no such element
@throws ClassCastException if the specified element cannot be
compared with the elements currently in the set
@throws NullPointerException if the specified element is null
and this set does not permit null elements
Returns the greatest element in this set strictly less than the given element, or {@code null} if there is no such element.
@param e the value to match @return the greatest element less than {@code e}, or {@code null} if there is no such element @throws ClassCastException if the specified element cannot be compared with the elements currently in the set @throws NullPointerException if the specified element is null and this set does not permit null elements