Unwrapped nil value in swiftui

I have an issue with unwrapped nil value in swiftui. I got the following error when I try to preview the class, "Runner crashed due to implicitly unwrapped optional in SignUpVC.swift at line 29".

The code is as following:

import UIKit import SwiftUI import PhotosUI

class SignUpVC: UIViewController {
    
    
    struct ContentView: View {

    @State private var showSheet: Bool = false
    @State private var showImagePicker: Bool = false
    @State private var sourceType: UIImagePickerController.SourceType = .camera
    
    @State private var image: UIImage?
    
        var body: some View {
            
            NavigationView {
                
                VStack {
                    
                    Image(uiImage: image ?? UIImage(named: "placeholder")!)
                        .resizable()
                        .frame(width: 300, height: 300)
                    
                    Button("Choose Picture") {
                        self.showSheet = true
                    }.padding()
                        .actionSheet(isPresented: $showSheet) {
                            ActionSheet(title: Text("Select Photo"),
                                        message: Text("Choose"), buttons: [
                                            .default(Text("Photo library")) {
                                                self.showImagePicker = true
                                                self.sourceType = .photoLibrary
                                            },
                                            .default(Text("Camera")) {
                                                self.showImagePicker = true
                                                self.sourceType = .camera
                                            },
                                            .cancel()
                                        ])
                        }
                }
                
                .navigationBarTitle("Camera Demo")
                
            }.sheet(isPresented: $showImagePicker) {
                ImagePicker(image: self.$image, isShown: self.$showImagePicker, sourceType: self.sourceType)
        }
    }
}
        

        
struct ContentView_Previews: PreviewProvider {
    static var previews: some View{
        ContentView()
    }
}
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .blue
        
    
}

}

How do i solve this problem?

Xcode crash every time I try to run the preview mode, and I got an error rapport from the system.