src/main/java/org/organicdesign/fp/collections/PersistentTreeMap.java
@Override public K lastKey() {
        UnEntry<K,V> max = last();
        if (max == null) {
            throw new NoSuchElementException("this map is empty");
        }
        return max.getKey();
    }
@Override public K lastKey() {
        UnEntry<K,V> max = last();
        if (max == null) {
            throw new NoSuchElementException("this map is empty");
        }
        return max.getKey();
    }
@ Override public K lastKey ( ) { UnEntry < K , V > max = last ( ) ; if ( max == null ) { throw new NoSuchElementException ( "this map is empty" ) ; } return max . getKey ( ) ; }
Returns the last key in this map or throws a NoSuchElementException if the map is empty.
Returns the last key in this map or throws a NoSuchElementException if the map is empty .