Error parsing a Json

When I parse a Json downloaded from here I get the following error:

  

Error: Error Domain = NSCocoaErrorDomain Code = 3840 "Unterminated string   around character 6464. "UserInfo = {NSDebugDescription = Unterminated   string around character 6464.} Error: Error Domain = NSCocoaErrorDomain   Code = 3840 "JSON text did not start with array or object and option to   allow fragments not set. "UserInfo = {NSDebugDescription = JSON text did   not start with array or object and option to allow fragments not set.}

I do not understand why, but following these steps:

Now, if I do it again with the same id the error does not come out anymore. If I use another id the next time, I will jump again until I repeat it again with the previous id .

Code:

class SearchPokemonDaoJson: NSObject,SearchPokemonDao, NSURLSessionDataDelegate {

    private let POKE_API = "http://pokeapi.co/api/v1/pokemon"
    private var session: NSURLSession = NSURLSession()
    private var task: NSURLSessionTask?

    private var hasFinished = 0
    private var pokemon: Pokemon?

    override init() {
        super.init()
        let config = NSURLSessionConfiguration.defaultSessionConfiguration()
        session = NSURLSession(configuration: config, delegate: self, delegateQueue: NSOperationQueue())
    }

    func search(ByID id: Int) -> Pokemon? {
        downloadBaseJson(NSURL(string: "\(POKE_API)/\(id)/")!)
        let before = CFDateGetAbsoluteTime(NSDate())
        while hasFinished != 2 {
            if ( (CFDateGetAbsoluteTime(NSDate()) - before) > 12000000000) {//5 Segundos.
                return nil
            }
        }
        return pokemon
    }

    func search(ByName name: String) -> Pokemon? {
        downloadBaseJson(NSURL(string: "\(POKE_API)/\(name)/")!)
        let before = CFDateGetAbsoluteTime(NSDate())
        while hasFinished != 2 {
            if ( (CFDateGetAbsoluteTime(NSDate()) - before) > 12000000000) {//5 Segundos.
                return nil
            }
        }
        return pokemon
    }

    private func makePokemon(From jsonDictionary: [String:AnyObject]) -> Pokemon? {
        let pokemonName = jsonDictionary["name"] as! String
        let pokemonID = jsonDictionary["national_id"] as! Int
        let pokemonTypes = convertTypes(jsonDictionary)
        downloadImageJson(extractSpriteURL(From: jsonDictionary)!)//Empieza a descargar el json de la imagen.
        let pokemon = Pokemon(id: pokemonID, type: pokemonTypes, name: pokemonName, goodAgainst: [PokemonType.Water], badAgainst: [PokemonType.Water])
        pokemon.evolution = extractEvolution(jsonDictionary)
        return pokemon
    }

    private func extractSpriteURL(From jsonDictionary: [String:AnyObject]) -> NSURL? {
        if let spritesArray = jsonDictionary["sprites"] {
            if let mainSprite = spritesArray[0] as? [String:String] {
                if let mainUrl = mainSprite["resource_uri"] {
                    return NSURL(string: "http://pokeapi.co\(mainUrl)")
                }
            }
        }
        return nil
    }

    private func convertTypes(jsonDictionary: [String:AnyObject]) -> [PokemonType] {
        var pokemonTypesS: [String] = []
        var arrayTypes = jsonDictionary["types"] as! Array<AnyObject>
        for index in 0..<arrayTypes.count {
            if let typeDictionary = arrayTypes[index] as? [String:AnyObject] {
                if let typeInfo = typeDictionary["name"] as? String {
                    pokemonTypesS.append(typeInfo)
                }
            }
        }
        return convertToArray(pokemonTypesS)
    }

    private func extractEvolution(jsonDictionary: [String:AnyObject] ) -> String? {
        if let evolutions = jsonDictionary["evolutions"] as? Array<AnyObject> {
            if !evolutions.isEmpty {
                if let evolution = evolutions[0] as? [String:AnyObject] {
                    if let evolutionTo = evolution["to"] as? String {
                        return evolutionTo
                    }
                }
            }
        }
        return nil
    }

    private func downloadImageJson(url: NSURL) {
        let task = session.dataTaskWithURL(url)
        task.taskDescription = "downloadPokemonImageJson"
        task.resume()
    }

    private func downloadImage(url:NSURL) {
        let task = session.dataTaskWithURL(url)
        task.taskDescription = "downloadPokemonImage"
        task.resume()
    }

    private func downloadBaseJson(url:NSURL) {
        hasFinished = 0
        task = session.dataTaskWithURL(url)
        task?.taskDescription = "downloadPokemonJson"
        task?.resume()
    }



    func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
        if dataTask.taskDescription == "downloadPokemonJson" {
            do {
                let jsonDictionary = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves) as? [String:AnyObject]
                pokemon = makePokemon(From: jsonDictionary!)
                self.hasFinished += 1
            } catch let error {
                print("Error: \(error)")
            }

        } else if dataTask.taskDescription == "downloadPokemonImageJson" {
            do {
                if let jsonDictionary = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves) as? [String:AnyObject] {
                    if let url = jsonDictionary["image"] as? String {
                        downloadImage(NSURL(string: "http://pokeapi.co\(url)")!)
                    }
                }
            } catch let error {
                print("Error extrayendo el main url para el sprite. \(error) ")
            }
        } else if dataTask.taskDescription == "downloadPokemonImage" {
            if let pokemon = pokemon {
                pokemon.sprite = UIImage(data: data)
                self.hasFinished += 1
            }
        }    }

    func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
        if task.taskDescription == "downloadPokemonJson" {
            if error != nil {
                print("Terminó de descargar la data con un error: \(error?.localizedDescription)")
            }
        }
    }

    func URLSession(session: NSURLSession, didBecomeInvalidWithError error: NSError?) {//error
        if (error != nil) {
            print("Error descargando el json de pokeapi: \(error?.description)")
        }
    }

}