Swift Error: EXC BAD INSTRUCTION code=EXCI386 for userid - swift

Question

I am writing an app login page when I countered this error. I do not know how to debug it so I am asking where I coded wrong. I got a problem on the keychain wrapper code:
KeychainWrapper.standard.set((user?.uid)!,forKey: "uid")
I am following a YouTube tutorial on Swift 4, the most updated version. However, it seems this line of code has some problems, therefore I would like to know the problem in the whole code, whether I missed I bracket or failed to import.
import UIKit
import Firebase
import FirebaseAuth
import FirebaseDatabase
import FirebaseCore
import SwiftKeychainWrapper
import FirebaseStorage
class ViewController: UIViewController {
#IBOutlet weak var usernameField: UITextField!
#IBOutlet weak var emailField: UITextField!
#IBOutlet weak var passwordField: UITextField!
#IBOutlet weak var userimageview: UIImageView!
var imagePicker: UIImagePickerController!
var selectedImage = UIImage()
override func viewDidLoad() {
super.viewDidLoad()
imagePicker = UIImagePickerController()
imagePicker.allowsEditing = true
imagePicker.delegate = self
}
override func viewDidAppear(_ animated: Bool) {
if KeychainWrapper.standard.object(forKey: "KEY_UID") != nil {
self.performSegue(withIdentifier: "toFeed", sender: nil)
}
}
func storeuserdata(userId: String) {
if let imageData = UIImageJPEGRepresentation(selectedImage, 0.2) {
Storage.storage().reference().putData(imageData, metadata: nil) { (metadata, error) in
guard let metadata = metadata else {
// Uh-oh, an error occurred!
return
}
// Metadata contains file metadata such as size, content-type, and download URL.
let downloadURL = metadata.downloadURL
Database.database().reference().child("users").child(userId).setValue(["username": self.usernameField.text!,"userImg": downloadURL
])
}
}
}
#IBAction func signinpressed(_ sender: Any) {
if let email = emailField.text, let password = passwordField.text {
Auth.auth().createUser(withEmail: email, password: password) { (user, error) in
if error != nil && (self.usernameField.text?.isEmpty)! && self.userimageview.image != nil {
Auth.auth().createUser(withEmail: email, password: password) { (user, error) in
self.storeuserdata(userId: (user?.uid)!)
KeychainWrapper.standard.set((user?.uid)!,forKey: "uid")
self.performSegue(withIdentifier: "toFeed", sender: nil)
}
}else {
KeychainWrapper.standard.set((user?.uid)!,forKey: "uid")
self.performSegue(withIdentifier: "toFeed", sender: nil)
}
}
}
}
#IBAction func getPhoto (_ sender: AnyObject) {
present(imagePicker, animated: true, completion: nil)
}
}
extension ViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate{
func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [String : Any]) {
if let image = info[UIImagePickerControllerEditedImage] as? UIImage {
selectedImage = image
}
imagePicker.dismiss(animated: true, completion: nil)
}
}