Error when clicking 'Start your adventure' button, after creating the closure for artworkView

mport UIKit

extension NSAttributedString {
    var stringRange: NSRange {
        return NSMakeRange(0, self.length)
    }
}

extension Story {
    var attributedText: NSAttributedString {
        let attributedString = NSMutableAttributedString(string: text)

        let paragraphStyle = NSMutableParagraphStyle()
        paragraphStyle.lineSpacing  = 10

        attributedString.addAttribute(NSAttributedStringKey.paragraphStyle, value: paragraphStyle , range: attributedString.stringRange)

        return attributedString
    }
}

extension Page {
    func story(attributed: Bool) -> NSAttributedString {
        if attributed == true {
            return story.attributedText
        } else {
            return NSAttributedString(string: story.text)
        }
    }
}

class PageController: UIViewController {

    var page: Page?

    // MARK: User Interface Properties

    lazy var artworkView: UIImageView = {
        let imageView = UIImageView()
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.image = self.page?.story.artwork

        return imageView
    }()

    let storyLabel: UILabel = {
        let label = UILabel()
        label.translatesAutoresizingMaskIntoConstraints = false
        label.numberOfLines = 0

        return label
    }()

    let firstChoiceButton: UIButton = {
        let button = UIButton(type: .system)
        button.translatesAutoresizingMaskIntoConstraints = false
        return button
    }()

    let secondChoiceButton: UIButton = {
        let button = UIButton(type: .system)
        button.translatesAutoresizingMaskIntoConstraints = false
        return button
    }()

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    init(page: Page) {
        self.page = page
        super.init(nibName: nil, bundle: nil)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        if let page = page {

            storyLabel.attributedText = page.story(attributed: true)

            if let firstChoice = page.firstChoice {
                firstChoiceButton.setTitle(firstChoice.title, for: .normal)
                firstChoiceButton.addTarget(self, action: #selector(PageController.loadFirstChoice), for: .touchUpInside)
            } else {
                firstChoiceButton.setTitle("Play Again", for: .normal)
                firstChoiceButton.addTarget(self, action: #selector(PageController.playAgain), for: .touchUpInside)
            }

            if let secondChoice = page.secondChoice {
                secondChoiceButton.setTitle(secondChoice.title, for: .normal)
                secondChoiceButton.addTarget(self, action: #selector(PageController.loadSecondChoice), for: .touchUpInside)
            }
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()

    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()

        NSLayoutConstraint.activate ([
            artworkView.topAnchor.constraint(equalTo: view.topAnchor),
            artworkView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            artworkView.rightAnchor.constraint(equalTo: view.rightAnchor),
            artworkView.leftAnchor.constraint(equalTo: view.leftAnchor),
        ])

        NSLayoutConstraint.activate([
            storyLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16.0),
            storyLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -16.0),
            storyLabel.topAnchor.constraint(equalTo: view.centerYAnchor, constant: -48.0),
        ])

        NSLayoutConstraint.activate([
            firstChoiceButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            firstChoiceButton.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -80.0)
            ])

        NSLayoutConstraint.activate([
            secondChoiceButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            secondChoiceButton.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -32)
            ])
    }

    @objc func loadFirstChoice() {
        if let page = page, let firstChoice = page.firstChoice {
            let nextPage = firstChoice.page
            let pageController = PageController.init(page: nextPage)

            navigationController?.pushViewController(pageController, animated: true)
        }
    }

    @objc func loadSecondChoice() {
        if let page = page, let secondChoice = page.secondChoice {
            let nextPage = secondChoice.page
            let pageController = PageController.init(page: nextPage)

            navigationController?.pushViewController(pageController, animated: true)
        }
    }

    @objc func playAgain() {
        navigationController?.popToRootViewController(animated: true)
    }


}