         case created
         case currentPeriodEnd = "current_period_end"
         case currentPeriodStart = "current_period_start"
-        case customerId = "customer"
+        case customer
         case daysUntilDue = "days_until_due"
         case discount
         case endedAt = "ended_at"

    public var created: Date?
    public var currentPeriodEnd: Date?
    public var currentPeriodStart: Date?
    public var customerId: String?
    public var daysUntilDue: Int?
    public var discount: StripeDiscount?
    public var endedAt: Date?

    var created: Date? { get }
    var currentPeriodEnd: Date? { get }
    var currentPeriodStart: Date? { get }
    var customer: String? { get }
    var daysUntilDue: Int? { get }
    var discount: D? { get }
    var endedAt: Date? { get }
