Error when wanting to parse JSON

Hello I have a query to run my application gives me the following error and I'm not discovering that you should greatly appreciate your help !. From already thank you very much! I attach part of my code

import UIKit
import Alamofire



extension MockData {

    static func index(completion: @escaping ([MockData]) -> Void) {

             Alamofire.request("https://www.dropbox.com/s/fem028u5ok95270/Clases.json?dl=1") .responseJSON { (response) in
            print(response)
            var users = [MockData]()
            if let objects = response.result.value {
                let json = objects as! NSDictionary
                let list = json["Horarios"] as? [[String: AnyObject]]

            for object in list! {
                users.append(MockData(dictionary: object))
            }
            }
            completion(users)

        }

    }
}

My Class MockData.Swift

import UIKit

class MockData: NSObject {

var id : String?
var dia : DiasClases?
var materia : String?
var horario : String?
var seccion : String?
var profesor : String?
//var aula : String?
//var obs : String?
var HorarioArray = [MockData]()


init(dictionary: [String: AnyObject]){

    self.id = dictionary["id"] as? String
    self.dia = dictionary["dia"] as? DiasClases
    self.materia = dictionary["materia"] as? String
    self.seccion = dictionary["seccion"] as? String
    self.profesor = dictionary["profesor"] as? String
    //self.aula = dictionary["aula"] as? String
    //self.obs = dictionary["obs"] as? String

}


}

enum DiasClases {
case Lunes
case Martes
case Miercoles
case Jueves
case Viernes
case Sabado

static func AllValues() -> [DiasClases] {
    return [Lunes, Martes, Miercoles, Jueves, Viernes, Sabado]
}
}