mpty set", and as such does
        not behave like a "zero" object in the mathematical sense. We may
        change that in the future (with a deprecation period).

    The null bbox is the identity for intersections

        >>> Bbox.intersection(Bbox([[1, 1], [3, 7]]), Bbox.null())
        Bbox([[1.0, 1.0], [3.0, 7.0]])

    except with itself, where it returns the full space.

        >>> Bbox.intersection(Bbox.null(), Bbox.null())
        Bbox([[-inf, -inf], [inf, inf]])

    A union containing null will always return the full space (not the other
    set!)

        >>> Bbox.union([Bbox([[0, 0], [0, 0]]), Bbox.null()])
        Bbox([[-inf, -inf], [inf, inf]])
    c