Stripe error: STPToken? is not a subtype of STPToken

Question

I am implementing Stripe in swift, and I am now trying to get the token from the card that was input. Like this :

var Client : STPAPIClient?
Client?.createTokenWithCard(card, completion: { (token: STPToken!, error: NSError!) -> Void in

})

and I am getting the error:

STPToken? is not a subtype of STPToken

Any ideas would be great, thanks!