      - parameter encoding:   The encoding to use for the parameters; .URL by default.
      - parameter headers:    The headers to be added to the request; nil by default.
      
-     - returns: A NSMutableURLRequest instance.
+     - returns: A URLRequest instance.
      */
-    final public func GET(_ url: URLConvertible, parameters: [String : AnyObject]? = nil, encoding: ParameterEncoding = URLEncoding(), headers: HTTPHeaders? = nil) -> URLRequestConvertible? {
+    final public func GET(_ url: URLConvertible, parameters: [String : AnyObject]? = nil, encoding: ParameterEncoding = URLEncoding(), headers: HTTPHeaders? = nil) -> URLRequest? {
         
         return request(.get, url, parameters: parameters, encoding: encoding, headers: headers)
     }

     - parameter encoding:   The encoding to use for the parameters; .JSON by default.
     - parameter headers:    The headers to be added to the request; nil by default.
     
     - returns: A NSMutableURLRequest instance.
     */
    final public func POST(_ url: URLConvertible, parameters: [String : AnyObject]? = nil, encoding: ParameterEncoding = JSONEncoding(), headers: HTTPHeaders? = nil) -> URLRequestConvertible? {
        
        return request(.post, url, parameters: parameters, encoding: encoding, headers: headers)
    }
}

     - parameter method:     The HTTP method for the request; GET by default.
     - parameter url:        The URL for the request
     - parameter parameters: The parameters to be added to the request; nil by default.
     - parameter encoding:   The encoding to use for the parameters; `URLEncoding` by default.
     - parameter headers:    The headers to be added to the request; nil by default.
     
     - returns: A URLRequest instance.
     */
    final public func request(_ method: Alamofire.HTTPMethod = .get, _ url: URLConvertible, parameters: [String : AnyObject]? = nil, encoding: ParameterEncoding = URLEncoding(), headers: HTTPHeaders? = nil) -> URLRequest? {

        do {
            let urlRequest = try URLRequest(url: url, method: method, headers: headers)
