public static <E> PCollectionsImmutableSet<E> empty() {
        return new PCollectionsImmutableSet<>(HashTreePSet.empty());
    }
@return a wrapped hash-based persistent set that is empty
@param <E> the element type
server-common/src/main/java/org/apache/kafka/server/immutable/pcollections/PCollectionsImmutableSet.java