xcode 予期せぬnilが見つかる

現在，下記リンクを参考にリアルタイムでの顔認識アプリのデモを製作しております．
https://qiita.com/TakahiroYamamoto/items/e970658a98a4e659cf9e

しかしながら，xcodeでの開発経験がなく，一つのエラー解決に多大な時間が掛っています．
エラーメッセージは
Fatal error: Unexpectedly found nil while unwrapping an Optional value
となっております．

プロジェクト開始後変更したファイルは下記二点のみです．
エラーメッセージは，一つ目のファイル(ViewController.swift)内の「エラー箇所」とコメントした分に対応付けされています．

不必要なnilがエラーの原因担っていることは分かったのですが，そのnilの正体がどこで宣言されたものであるのか理解できません．

検討の付く方，ご教示いただけないでしょうか．
よろしくお願い致します．

swiftコード
ViewController.swift

swift
1//  
2//  ViewController.swift
3//  get_face_to_hello
4//
5//  Created by name on 2019/02/18.
6//  Copyright © 2019年 name. All rights reserved.
7//
8
9import UIKit
10
11class ViewController: UIViewController {
12
13    override func viewDidLoad() {
14        super.viewDidLoad()
15        // Do any additional setup after loading the view, typically from a nib.
16    }
17
18    var faceTracker:FaceTracker? = nil;
19    @IBOutlet var cameraView :UIView!//viewController上に一つviewを敷いてそれと繋いでおく
20    
21    var rectView = UIView()
22    override func viewDidAppear(_ animated: Bool) {
23        super.viewDidAppear(animated)
24        self.rectView.layer.borderWidth = 3//四角い枠を用意しておく
25        self.view.addSubview(self.rectView)
26        faceTracker = FaceTracker(view: self.cameraView, findface:{arr in // エラー箇所
27            let rect = arr[0];//一番の顔だけ使う
28            self.rectView.frame = rect;//四角い枠を顔の位置に移動する
29        })
30    }
31
32}
33

FaceTracker.swift

swift
1import UIKit
2import AVFoundation
3
4class FaceTracker: NSObject,AVCaptureVideoDataOutputSampleBufferDelegate {
5    let captureSession = AVCaptureSession()
6    let videoDevice = AVCaptureDevice.default(for: AVMediaType.video)
7    let audioDevice = AVCaptureDevice.default(for: AVMediaType.audio)
8    
9    var videoOutput = AVCaptureVideoDataOutput()
10    var view:UIView
11    private var findface : (_ arr:Array<CGRect>) -> Void
12    required init(view:UIView, findface: @escaping (_ arr:Array<CGRect>) -> Void)
13    {
14        self.view=view
15        self.findface = findface
16        super.init()
17        self.initialize()
18    }
19    
20    
21    func initialize()
22    {
23        //各デバイスの登録(audioは実際いらない)
24        do {
25            let videoInput = try AVCaptureDeviceInput(device: self.videoDevice!) as AVCaptureDeviceInput
26            self.captureSession.addInput(videoInput)
27        } catch let error as NSError {
28            print(error)
29        }
30        do {
31            let audioInput = try AVCaptureDeviceInput(device: self.audioDevice!) as AVCaptureInput
32            self.captureSession.addInput(audioInput)
33        } catch let error as NSError {
34            print(error)
35        }
36        
37        self.videoOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as AnyHashable as! String : Int(kCVPixelFormatType_32BGRA)]
38        
39        //フレーム毎に呼び出すデリゲート登録
40        //let queue:DispatchQueue = DispatchQueue(label:"myqueue",attribite: DISPATCH_QUEUE_SERIAL)
41        let queue:DispatchQueue = DispatchQueue(label: "myqueue", attributes: .concurrent)
42        self.videoOutput.setSampleBufferDelegate(self, queue: queue)
43        self.videoOutput.alwaysDiscardsLateVideoFrames = true
44        
45        self.captureSession.addOutput(self.videoOutput)
46        
47        let videoLayer : AVCaptureVideoPreviewLayer = AVCaptureVideoPreviewLayer(session: self.captureSession)
48        videoLayer.frame = self.view.bounds
49        videoLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill
50        
51        self.view.layer.addSublayer(videoLayer)
52        
53        //カメラ向き
54        for connection in self.videoOutput.connections {
55            let conn = connection
56            if conn.isVideoOrientationSupported {
57                conn.videoOrientation = AVCaptureVideoOrientation.portrait
58            }
59        }
60        
61        self.captureSession.startRunning()
62    }
63    
64    func imageFromSampleBuffer(sampleBuffer: CMSampleBuffer) -> UIImage {
65        //バッファーをUIImageに変換
66        let imageBuffer: CVImageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)!
67        CVPixelBufferLockBaseAddress(imageBuffer, CVPixelBufferLockFlags(rawValue: 0))
68        let baseAddress = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0)
69        let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer)
70        let width = CVPixelBufferGetWidth(imageBuffer)
71        let height = CVPixelBufferGetHeight(imageBuffer)
72        
73        let colorSpace = CGColorSpaceCreateDeviceRGB()
74        let bitmapInfo = (CGBitmapInfo.byteOrder32Little.rawValue | CGImageAlphaInfo.premultipliedFirst.rawValue)
75        let context = CGContext(data: baseAddress, width: width, height: height, bitsPerComponent: 8, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo)
76        let imageRef = context!.makeImage()
77        
78        CVPixelBufferUnlockBaseAddress(imageBuffer, CVPixelBufferLockFlags(rawValue: 0))
79        let resultImage: UIImage = UIImage(cgImage: imageRef!)
80        return resultImage
81    }
82    
83    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection)
84    {
85        //同期処理（非同期処理ではキューが溜まりすぎて画面がついていかない）
86        DispatchQueue.main.sync(execute: {
87            
88            //バッファーをUIImageに変換
89            let image = self.imageFromSampleBuffer(sampleBuffer: sampleBuffer)
90            let ciimage:CIImage! = CIImage(image: image)
91            
92            //CIDetectorAccuracyHighだと高精度（使った感じは遠距離による判定の精度）だが処理が遅くなる
93            let detector : CIDetector = CIDetector(ofType: CIDetectorTypeFace, context: nil, options:[CIDetectorAccuracy: CIDetectorAccuracyLow] )!
94            let faces : NSArray = detector.features(in: ciimage) as NSArray
95            
96            if faces.count != 0
97            {
98                var rects = Array<CGRect>();
99                var _ : CIFaceFeature = CIFaceFeature()
100                for feature in faces {
101                    
102                    // 座標変換
103                    var faceRect : CGRect = (feature as AnyObject).bounds
104                    let widthPer = (self.view.bounds.width/image.size.width)
105                    let heightPer = (self.view.bounds.height/image.size.height)
106                    
107                    // UIKitは左上に原点があるが、CoreImageは左下に原点があるので揃える
108                    faceRect.origin.y = image.size.height - faceRect.origin.y - faceRect.size.height
109                    
110                    //倍率変換
111                    faceRect.origin.x = faceRect.origin.x * widthPer
112                    faceRect.origin.y = faceRect.origin.y * heightPer
113                    faceRect.size.width = faceRect.size.width * widthPer
114                    faceRect.size.height = faceRect.size.height * heightPer
115                    
116                    rects.append(faceRect)
117                }
118                self.findface(rects)
119            }
120        })
121    }
122}
123