An extension for Alamofire to return AEXMLDocument as response

Alamofire+AEXML.swift

extension Request {
    public func responseAEXMLDocument(completionHandler: (NSURLRequest, NSHTTPURLResponse?, AEXMLDocument?, NSError?) -> Void) -> Self {
        return response { (request: NSURLRequest, response: NSHTTPURLResponse?, responseObj: AnyObject?, responseError: NSError?) -> Void in
            var parse_error: NSError?
            if let obj = responseObj as? NSData, xml = AEXMLDocument(xmlData: obj, error: &parse_error) {
                if let aerror = parse_error{
                    completionHandler(request, response, nil, aerror)
                } else {
                    completionHandler(request, response, xml, responseError)
                }
            } else {
                completionHandler(request, response, nil, responseError)
            }
        }
    }
}

This is currently written in Swift 1.2