Can Arktype create discriminated unions based on whether a key exists?

 typescript
const MasterSkinItem = BaseItem.merge({
    "+": "reject",
    type: "'skin'",
    masterItem: "true",

    skin: "string",
    short: "string",
    weapon: WeaponUnion,

    minPrice: "number.integer >=0",
    stattrakAvailable: "boolean = false",
    souvenirAvailable: "boolean = false",
    qualities: type("1 | 2 | 3 | 4 |5").array().or(["null"]),
});

const SkinItem = BaseItem.merge({
    "+": "reject",
    type: "'skin'",
    // "masterItem?": "false",
    skin: "string",
    short: "string",
    weapon: WeaponUnion,

    "weight?": "number",
    souvenir: "boolean = false",
    stattrak: "boolean = false",
    quality: type("1 | 2 | 3 | 4 |5").optional(),
});
const Skinish = MasterSkinItem.or(SkinItem);