Navigation Controller Nil

// This is for a Slide Menu
// Container Controller

import Foundation
import UIKit

class ContainerController: UIViewController {
    // MARK: Properties
    private var aboutController: AboutViewController!
    private var slideController: SlideController!
    private var homeController: HomeScreenController!
    public var homeNavigationController: UINavigationController?
    private var centerController: UIViewController!
    // Delegates
    public weak var blurEffectBooleanDelegate: BlurEffectBooleanProtocol?
    public weak var homeCellSelectionDelegate: HomeCellSelectionProtocol?
    // Slide Menu Toggle
    private var isOpen: Bool = false

    override func viewDidLoad() {
        super.viewDidLoad()
        setup()
        configureHomeNavigationController()
    }


    private func setup() {
        view.backgroundColor = UIColor(red: 65/255, green: 0, blue: 0, alpha: 1.0)
    }


    private func configureHomeNavigationController() {
        homeController = HomeScreenController()
        homeController.handleSlideMenuDelegate = self
        self.homeCellSelectionDelegate = homeController
        homeNavigationController = UINavigationController(rootViewController: homeController)
        centerController = homeNavigationController
        view.addSubview(centerController.view)
        addChild(centerController)
        centerController.didMove(toParent: self)
    }


    private func configureAboutController() {
        aboutController = AboutViewController()
        view.insertSubview(aboutController.view, at: 0)
        addChild(aboutController)
        aboutController.didMove(toParent: self)
    }

    // MARK: TEST - Status: DONE
    fileprivate func addSlideMenu() {
        if slideController == nil {
            slideController = SlideController()
            view.insertSubview(slideController.view, at: 0)
            addChild(slideController)
            slideController.didMove(toParent: self)
        }
    }

    // MARK: TEST - Status: DONE
    fileprivate func removeSlideMenu() {
        if slideController != nil {
            slideController.view.removeFromSuperview()
            slideController.willMove(toParent: nil)
            slideController.removeFromParent()
            slideController = nil
        }
    }


    public func shouldExpandSlideMenu(_ expanded: Bool) {
        if expanded {
            UIView.animate(withDuration: 0.6, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
                self.centerController.view.frame.origin.x = self.centerController.view.frame.width - 100
                self.blurEffectBooleanDelegate?.blurEnabled = false
                self.addSlideMenu()
            }, completion: nil)
        } else {
            UIView.animate(withDuration: 0.6, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 0.5, options: .curveEaseInOut, animations: {
                self.centerController.view.frame.origin.x = 0
                self.blurEffectBooleanDelegate?.blurEnabled = true
            }, completion: { _ in
                self.removeSlideMenu()
            })
        }
    }

}

extension ContainerController: HandleSlideMenuProtocol {
    func handleSlideToggle() {
        isOpen = !isOpen
        shouldExpandSlideMenu(isOpen)
    }

}

extension ContainerController: InnerSelectedCellProtocol {
    func selectedCell(isSelected: Bool) {
        if isSelected == true {
            print("Pushing")
            homeController = HomeScreenController()
            self.homeCellSelectionDelegate = homeController
            homeCellSelectionDelegate?.pushToDetailController()
        }
    }
}

// My testing Protocol to see if it would work.
import Foundation
import UIKit

protocol HomeCellSelectionProtocol: class {
    func pushToDetailController()
}


// Home Controller which contains the collectionView which I try to push when I select an item. It would push before I refactored it to add the slide menu. Unrelated functions and properties removed. The navigationController isn't nil only until I'm trying to pushViewController()

import UIKit
import Foundation

class HomeScreenController: UIViewController, BlurEffectBooleanProtocol, HomeCellSelectionProtocol {
    // References / Properties
    public lazy var detailController = DetailViewController()
    public lazy var launchScreenController = LaunchScreenController()
    public lazy var containerController = ContainerController()
    // Delegates
    public weak var launchScreenDelegate: LaunchScreenProtocol?
    public weak var castMovieIdDelegate: CastMovieIdProtocol?
    public weak var handleSlideMenuDelegate: HandleSlideMenuProtocol?

    override func viewDidLoad() {
        super.viewDidLoad()
        initialSetup()
        makeApiCall()
    }


    private func makeApiCall() {
        launchScreenDelegate = launchScreenController
        navigationController?.pushViewController(launchScreenController, animated: false)
        makeRequestToServer()
    }


    private func makeRequestToServer() {
        apiManager.makeApiRequest {
            self.leftBarButtonView()
            self.mainView.refreshControl.endRefreshing()
            self.launchScreenDelegate?.isLoadingFinished(true)
            DispatchQueue.main.async { [weak self] in
                guard let self = self else { return }
                for cell in self.mainView.collectionView.visibleCells {
                    if let cell = cell as? MovieCollectionViewCell {
                        cell.innerCollectionView.reloadData()
                    }
                }
            }
        }
    }

    // MARK: - Setup
    private func initialSetup() {
        // Navigation Controller
        navigationController?.isNavigationBarHidden = false
        let titleAttributes = [NSAttributedString.Key.foregroundColor: UIColor.white]
        navigationController?.navigationBar.titleTextAttributes = titleAttributes
        navigationController?.navigationBar.topItem?.title = "Movies"
        navigationController?.navigationBar.prefersLargeTitles = true
        navigationController?.hidesBarsOnSwipe = false
        navigationController?.navigationBar.largeTitleTextAttributes = [NSAttributedString.Key.font: UIFont(name: "HelveticaNeue-Thin", size: 50)!, NSAttributedString.Key.foregroundColor: UIColor(red: 225/255, green: 225/255, blue: 225/255, alpha: 1.0)]
        navigationController?.navigationItem.leftBarButtonItem = nil
        navigationController?.navigationBar.setBackgroundImage(UIImage(), for: .default)
        navigationController?.navigationBar.shadowImage = UIImage()
        navigationController?.navigationBar.isTranslucent = true
        // Delegates
        containerController.blurEffectBooleanDelegate = self
        // Blur Effect
        blurEffectView.effect = mainView.blurEffect
        blurEffectView.frame = view.bounds
        blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        blurEffectView.isHidden = blurEnabled
        blurEffectView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(blurEffectTap)))
        view.insertSubview(blurEffectView, at: 1)
        // Refresh Control
        mainView.refreshControl.addTarget(self, action: #selector(refreshView(_:)), for: .valueChanged)
    }


    private func leftBarButtonView() {
        navigationItem.leftBarButtonItem = UIBarButtonItem(image: mainView.categoryImageView.image, style: .plain, target: self, action: #selector(categoryAction))
    }

    // MARK: Delegate Function for Selection of Cell
    func pushToDetailController() {
        print("Inside")
        displayingDetailController()
    }


    private func displayingDetailController() {
        // The navigationController is nil
        navigationController?.pushViewController(detailController, animated: true)
    }

} // Class end