public static <E extends Comparable<? super E>> PCollectionsImmutableNavigableSet<E> singleton(E e) {
        return new PCollectionsImmutableNavigableSet<>(TreePSet.singleton(e));
    }
@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