Swift4:カスタムTable ViewでFatal error: Unexpectedly found nil while unwrapping an Optional value

現在カスタムTableViewを作成しケースごとに分けて表示しています。
各LabelにはAPIを叩いて取得したJsonデータが代入されています。
NavigationControllerを追加し他ところif let price:String = store![indexPath.row].priceと他のtime,closeddayの部分で
Unexpectedly found nil while unwrapping an Optional valueとエラーが出ました。
NavigationControllerを追加する前は問題なく動いていました。
これはAPIを叩いて取得したJsonが読み込みが完了する前に強制アンラップしているのが原因でしょうか。
またその場合の対処はどうすればいいでしょうか。よろしくお願いします。

TableView
1    var store_id = ""
2    var store : [Store]?
3    var photoPath : [Store.photos]?
4    var tag : [Store.tags]?
5
6override func viewDidLoad() {
7        super.viewDidLoad()
8        
9        
10        //Collectiopn DetaSources
11        imageCollectionView.dataSource = self
12        imageCollectionView.delegate = self
13        
14        tagCollectionView.dataSource = self
15        tagCollectionView.delegate = self
16        
17        //UIView Shadow
18        let shadowPath = UIBezierPath(rect: UIView.bounds)
19        UIView.layer.masksToBounds = false
20        UIView.layer.shadowColor = UIColor.black.cgColor
21        UIView.layer.shadowOffset = .zero
22        UIView.layer.shadowOpacity = 0.2
23        UIView.layer.shadowPath = shadowPath.cgPath
24        
25        //Request API
26        let url = URL(string: "http://localhost:8000/store/api?store_id=" + store_id)
27        let request = URLRequest(url: url!)
28        let session = URLSession.shared
29        
30        let encoder: JSONEncoder = JSONEncoder()
31        encoder.dateEncodingStrategy = .iso8601
32        encoder.outputFormatting = .prettyPrinted
33        
34        session.dataTask(with: request){(data, response, error)in if error == nil,
35            let data = data,
36            let response = response as? HTTPURLResponse{
37            
38            let decoder: JSONDecoder = JSONDecoder()
39            decoder.dateDecodingStrategy = .iso8601
40            do {
41                
42                let json = try decoder.decode(Store.self, from: data)
43
44                if json != nil {
45                    print("JSON is Nil")
46                }else{
47                    print(json)
48                }
49                self.store = [json]
50                self.photoPath = json.photos
51                self.tag = json.tags
52                
53                if let imageURL = URL(string: "http://127.0.0.1:8000/photos/" + json.photos[0].path){
54                    DispatchQueue.global().async {
55                        let data = try? Data(contentsOf: imageURL)
56                        if let data = data {
57                            let image = UIImage(data: data)
58                            DispatchQueue.main.async {
59                                self.mainImage.image = image
60                            }
61                        }
62                    }
63                }
64                
65                DispatchQueue.main.async {
66                    self.nameLabel.text = json.name
67                    self.locationLabel.text = json.location
68                    
69                }
70                
71            } catch {
72                print("error:", error.localizedDescription)
73                
74            }
75            
76            }
77            
78            }.resume()
79}
80
81
82func numberOfSections(in tableView: UITableView) -> Int {
83        return 3
84    }
85    
86    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
87        switch section {
88        case 0:
89            return 1
90        case 1 :
91            return 1
92        case 2 :
93            return 1
94        default:
95            return 0
96        }
97    }
98
99func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
100        
101        let cell = UITableViewCell()
102        
103        switch indexPath.section {
104        case 0 :
105        //Price Cell
106        let priceCell = tableView.dequeueReusableCell(withIdentifier: "priceCell", for: indexPath) as? priceTableViewCell
107        
108        if let price:String = store![indexPath.row].price{
109            priceCell?.priceLabel.text! = price
110        }else{
111            priceCell?.priceLabel.text! = "-"
112        }
113        return priceCell!
114        
115        case 1 :
116        //timeCell
117            
118            let timeCell = tableView.dequeueReusableCell(withIdentifier: "timeCell", for: indexPath) as? timeTableViewCell
119            
120            if let time:String = store![indexPath.row].open_time{
121                timeCell?.timeLabel.text! = time
122            }else{
123                timeCell?.timeLabel.text! = "-"
124            }
125        return timeCell!
126        
127        case 2 :
128        //closedayCell
129        let closedayCell = tableView.dequeueReusableCell(withIdentifier: "closedayCell", for: indexPath) as? closedayTableViewCell
130        
131        if let closeday:String = store![indexPath.row].closed_day{
132            closedayCell?.closedayLabel.text! = closeday
133        }else{
134            closedayCell?.closedayLabel.text! = "-"
135        }
136
137        
138        return closedayCell!
139            
140        default :
141            print("Default Selected")
142        }
143        return cell
144    }