View遷移時に画像が渡せません。

下記のコードでsignal SIGABRTのエラーが出てしまいます。

view controller1

@IBOutlet weak var image1: UIImageView!
@IBOutlet weak var image2: UIImageView!

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let vc2 = segue.destination as! ViewController2
    vc2.image3 = self.image1.image
    vc2.image4 = self.image2.image
}

view controller2 (vc2)

@IBOutlet weak var image21: UIImageView!
@IBOutlet weak var image22: UIImageView!

var image3: UIImage?
var image4: UIImage?

override func viewDidLoad() {
    super.viewDidLoad()

    self.image21.image = image3
    self.image22.image = image4
}