Why does rejecting an Alamofire request with a custom error results in a PromiseKit: Unhandled Error: message

Question

I am using the following:

• Alamofire (3.1.4)
• PromiseKit (3.0.0)
• xCode Version 7.2.1 (7C1002)

I am rejecting an Alamofire request with the custom error below:

Error is the struct that provides convenience methods for creating custom alamofire NSErrors. I am using errorWithCode as shown below.

let error = Error.errorWithCode(Error.Code.InputStreamReadFailed, failureReason: "reason")
reject(error)

I have also tried the following:

reject(NSError(domain: "somedomain", code: 123, userInfo: [:]))

In either case I receive the following message in the xCode console: "...PromiseKit: Unhandled Error: Error Domain=com.alamofire.error Code=-6000 "reason" UserInfo={NSLocalizedFailureReason=reason}"

I am wondering if this is something I am doing wrong on my end or a bug?

Here is the complete function:

func getImageByID(imageID : String) -> Promise<UIImage> {
    return Promise { fulfill, reject in
        Alamofire.request(.GET, getImageURL(imageID)).responseData {response in
            if response.result.isSuccess {
                if response.data != nil {
                    if let image = UIImage(data: response.data!) {
                        fulfill(image)
                    } else if UIImage(data: response.data!) == nil {

                        let error = Error.errorWithCode(Error.Code.InputStreamReadFailed, failureReason: "reason")
                        reject(error)
                        //reject(NSError(domain: "somedomain", code: 123, userInfo: [:]))
                        //reject(NSError(domain: "somedomain", code: 123, userInfo: nil))
                    } else {
                      .....
                    }
                }
            } else {
                reject(response.result.error!)
            }
        }
    }
}

Any help is most appreciated!

Thanks!