@Override
    public String toString() {
        return "PCollectionsImmutableNavigableSet{" +
                "underlying=" + underlying() +
                '}';
    }
@param e the element
@return a wrapped tree-based persistent set that is empty
@param <E> the element type
server-common/src/main/java/org/apache/kafka/server/immutable/pcollections/PCollectionsImmutableNavigableSet.java