already set ! but get fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)

Question

I create a json like this and put it into website URL:

[{"categoryID":1,"parentID":0,"categoryName":"Tempat Makan","imageFile":"foodandbeverages.png","isTopCategory":false},{"categoryID":2,"parentID":0,"categoryName":"Mini Market","imageFile":"minimarket.png","isTopCategory":false},{"categoryID":3,"parentID":0,"categoryName":"ATM","imageFile":"atm.png","isTopCategory":false},{"categoryID":4,"parentID":0,"categoryName":"SPBU","imageFile":"gasstation.png","isTopCategory":false},{"categoryID":5,"parentID":0,"categoryName":"Penginapan","imageFile":"inn.png","isTopCategory":false},{"categoryID":6,"parentID":0,"categoryName":"Bengkel","imageFile":"workshop.png","isTopCategory":false},{"categoryID":7,"parentID":0,"categoryName":"Kesehatan","imageFile":"health.png","isTopCategory":false},{"categoryID":9,"parentID":0,"categoryName":"Percetakan","imageFile":"printing.png","isTopCategory":false},{"categoryID":10,"parentID":0,"categoryName":"Cafetaria","imageFile":"cafetaria.png","isTopCategory":false},{"categoryID":11,"parentID":0,"categoryName":"Bank","imageFile":"bank.png","isTopCategory":false},{"categoryID":13,"parentID":0,"categoryName":"Jasa","imageFile":"services.png","isTopCategory":false},{"categoryID":65,"parentID":0,"categoryName":"Tempat Belanja","imageFile":"shopping.png","isTopCategory":false},{"categoryID":66,"parentID":0,"categoryName":"Hiburan","imageFile":"entertainment.png","isTopCategory":false},{"categoryID":79,"parentID":0,"categoryName":"Perjalanan","imageFile":"travel.png","isTopCategory":false},{"categoryID":83,"parentID":0,"categoryName":"Tempat","imageFile":"places.png","isTopCategory":false},{"categoryID":89,"parentID":0,"categoryName":"Pendidikan","imageFile":"education.png","isTopCategory":false},{"categoryID":93,"parentID":0,"categoryName":"Kecantikan","imageFile":"beautyandspa.png","isTopCategory":false},{"categoryID":99,"parentID":0,"categoryName":"Rental","imageFile":"rent.png","isTopCategory":false},{"categoryID":105,"parentID":0,"categoryName":"Peliharaan","imageFile":"pet.png","isTopCategory":false}]

I try to put categoryID, categoryName and imageFile into collection view with code like these:

struct country
{
    var imageFile:String!
    var categoryName:String!
    var categoryID:Int!
    init(categoryID:Int, categoryName:String, imageFile:String)
    {
        self.imageFile = imageFile
        self.categoryName = categoryName
        self.categoryID = categoryID
    }
}

var Data:Array<  country > = Array < country >()

override func viewDidLoad() {
    super.viewDidLoad()
    collectionview.dataSource = self
    collectionview.delegate = self

    let layout:UICollectionViewFlowLayout = UICollectionViewFlowLayout()
    layout.sectionInset = UIEdgeInsets(top:1,left:10,bottom:10,right:10)
    layout.minimumInteritemSpacing = 5
    layout.minimumLineSpacing = 10

    collectionview.collectionViewLayout = layout

    get_data_from_url("http://domain/category.json")
}

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
{

    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as! CategoryCell


    let bcolor : UIColor = UIColor( red: 0.2, green: 0.2, blue:0.2, alpha: 0.3 )

    cell.layer.borderColor = bcolor.CGColor
    cell.layer.borderWidth = 0.5
    cell.layer.cornerRadius = 3

    cell.backgroundColor=UIColor.whiteColor()


    cell.text.text = "\(Data[indexPath.row].categoryID)"
    cell.country.text = Data[indexPath.row].categoryName
    let gambar_categorynya = "http://domain/category/\(Data[indexPath.row].imageFile)"
    print("gambar_categorynya:\(gambar_categorynya)")
    cell.imageCategory.image = UIImage(data: NSData(contentsOfURL: NSURL(string:"http://domain/category/\(Data[indexPath.row].imageFile)")!)!)
    return cell
}


func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
    return Data.count
}

func collectionView(collectionView: UICollectionView,
                    layout collectionViewLayout: UICollectionViewLayout,
                           sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {

    return CGSize(width: 100  , height: 50)

}

and extract json data like this:

func extract_json(data:NSString)
{
    var parseError: NSError?
    let jsonData:NSData = data.dataUsingEncoding(NSASCIIStringEncoding)!
    let json: AnyObject?
    do {
        json = try NSJSONSerialization.JSONObjectWithData(jsonData, options: [])
    } catch let error as NSError {
        parseError = error
        json = nil
    }
    if (parseError == nil)
    {
        if let countries_list = json as? NSArray
        {
            for (var i = 0; i < countries_list.count ; i++ )
            {
                if let country_obj = countries_list[i] as? NSDictionary
                {
                    if let country_image = country_obj["imageFile"] as? String
                    {
                        if let country_name = country_obj["categoryName"] as? String
                        {
                            if let country_code = country_obj["categoryID"] as? Int
                            {
                                let add_it = country(categoryID: country_code, categoryName: country_name, imageFile: country_image)
                                Data.append(add_it)
                            }
                        }
                    }
                }
            }
        }
    }
    do_refresh();
}


func do_refresh()
{
    dispatch_async(dispatch_get_main_queue(), {
        self.collectionview.reloadData()
        return
    })
}

func get_data_from_url(url:String)
{
    let httpMethod = "GET"
    let timeout = 15
    let url = NSURL(string: url)
    let urlRequest = NSMutableURLRequest(URL: url!,
                                         cachePolicy: .ReloadIgnoringLocalAndRemoteCacheData,
                                         timeoutInterval: 15.0)
    let queue = NSOperationQueue()
    NSURLConnection.sendAsynchronousRequest(
        urlRequest,
        queue: queue,
        completionHandler: {(response: NSURLResponse?,
            data: NSData?,
            error: NSError?) in
            if data != nil && error == nil{
                let json = NSString(data: data!, encoding: NSASCIIStringEncoding)
                self.extract_json(json!)
            }
        }
    )
}

my last looping print stop at gambar_categorynya:http://domain/category/travel.png

after that it thrown error : fatal error: unexpectedly found nil while unwrapping an Optional value (lldb)

and the error (red signal) at this line:

cell.imageCategory.image = UIImage(data: NSData(contentsOfURL: NSURL(string:"http://domain/category/\(Data[indexPath.row].imageFile)")!)!)

how to correct this?

info: imageFile always string so even i put string! it still trown me error fatal error: unexpectedly found nil while unwrapping an Optional value (lldb). I already got all categoryID and categoryName. this is collectionview cell:

class CategoryCell: UICollectionViewCell {
    @IBOutlet var text: UILabel!
    @IBOutlet var country: UILabel!
    @IBOutlet weak var imageCategory: UIImageView!
}