* @param map the map to create a stream from; if {@code null}, an empty stream is returned
     * @return a {@link StreamOf} containing the entries of the map, or an empty stream if the map is {@code null}
     */
    public static <K, V> StreamOf<Map.Entry<K, V>> stream(final Map<K, V> map) {
        return new StreamOf<>(() -> map != null ? map.entrySet().stream() : Collections.<K, V> emptyMap().entrySet().stream());
    }

    /**