Serializer error for Alamofire

I'm trying to write generic serializers for Alamofire, and I'm trying to figure out how I can get the response serializer generator to detect if there was an error, and instead return a custom error object (the server returns a dictionary of errors in this situation).

Any input would be appreciated!

Here's some sample code I'm currently using:

@objc public protocol ResponseObjectSerializable {
    init?(response: NSHTTPURLResponse, representation: AnyObject)
}

extension Alamofire.Request {
    public func responseObject<T: ResponseObjectSerializable>(completionHandler: (NSURLRequest, NSHTTPURLResponse?, T?, NSError?) -> Void) -> Self {
        let serializer: Serializer = { (request, response, data) in
            let JSONSerializer = Request.JSONResponseSerializer(options: .AllowFragments)
            let (JSON: AnyObject?, serializationError) = JSONSerializer(request, response, data)
            if response != nil && JSON != nil {
                        return (T(response: response!, representation: JSON!), nil)
                    } else {
                        return (nil, serializationError)
                    }
                }

        return response(serializer: serializer, completionHandler: { (request, response, object, error) in
            completionHandler(request, response, object, error)
        })
    }
}