div {
    // nulls should be omitted from evaluated lists
    a: (1, null, 2, null, 3);
    // but not from literal untouched lists
    b: 1, null, 2, null, 3;

    // entirely null lists become nothing
    c: 1 (null, null) 2;
    // empty properties aren't printed
    d: (null, null);
    // and it applies recursively
    e: (((null, 1, null), (null, 2), null), (3, null, (null, null)));
}