enum CodingKeys: String, CodingKey {
    case attributeCode = "attribute_code"
    case value = "value"
}

init(from decoder: Decoder) throws {
    let container = try decoder.singleValueContainer()
    if let x = try? container.decode([String].self) {
        self = .stringArray(x)
        return
    }
    if let x = try? container.decode(String.self) {
        self = .string(x)
        return
    }
    throw DecodingError.typeMismatch(ValueUnion.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for ValueUnion"))
}

func encode(to encoder: Encoder) throws {
    var container = encoder.singleValueContainer()
    switch self {
    case .string(let x):
        try container.encode(x)
    case .stringArray(let x):
        try container.encode(x)
    }
}