Method union

src/main/java/field/utility/Cuboid.java:27–31

(Cuboid r, Cuboid rect)

	}

	public static Cuboid union(Cuboid r, Cuboid rect) {
		if (r == null) return rect;
		if (rect == null) return r;
		return r.union(rect);
	}

	public Cuboid union(Cuboid r) {
		if (r == null) return this;