public static <K, V> MapStream<K, V> empty() {
        return new MapStream<>(Stream.empty());
    }
Constructs an empty {@code MapStream}.

@param <K>  key type
@param <V>  value type
@return     an empty {@code MapStream}
common-parent/mapstream/src/main/java/com/speedment/common/mapstream/MapStream.java