func signUp(_ email: String, usersname: String, password: String, data: Data!, loginHandler: LoginHandler?) {

    FIRAuth.auth()?.createUser(withEmail: email, password: password,  completion: { (user, error) in

        if error != nil {
            // Show error to user
            self.handleFirebaseErrors(err: error as! NSError, loginHandler: loginHandler)

        } else { // success creating user

            if user?.uid != nil { // if there is a valid user id

                // Store user to database
                self.setUserInfo(user, usersname: usersname, email: email, password: password, data: data!)

                // Log In the user
                self.login(email: email, password: password, loginHandler: loginHandler)
            }
        }
    })

}

func saveUser(_ user: FIRUser!, usersname: String, email: String, password: String) {

    // Create the user dictionary info
    let userInfo = ["email": user.email!, "password": password, "usersname": usersname, "uid": user.uid, "photoUrl": String(describing: user.photoURL!)]

    // create user reference
    let userRef = DataService.Instance.dbRef.child("riders").child(user.uid)

    // Save the user info in the database
    userRef.setValue(userInfo)

}

func login(email: String, password: String, loginHandler: LoginHandler?) {

    FIRAuth.auth()?.signIn(withEmail: email, password: password, completion: { (user, error) in

        if error != nil {
            self.handleFirebaseErrors(err: error as! NSError, loginHandler: loginHandler)
        } else {
            loginHandler?(nil, nil)
        }
    })

}

let userRef = DataService.Instance.dbRef.child("riders").child(usersname)

fatal error: unexpectedly found nil while unwrapping an Optional value

let imageUrl = String(user.photoUrl)

if FIRAuth.auth()?.currentUser == nil {

        let vc = UIStoryboard(name: "Rider", bundle: nil).instantiateViewController(withIdentifier: "Login")
        present(vc, animated: true, completion: nil)

    } else {

        dbRef.child("riders/(FIRAuth.auth()!.currentUser!.uid)").observe(.value, with: { (snapshot) in
            DispatchQueue.main.async(execute: {


                let user = User(snapshot: snapshot)
                self.username.text = user.usersname
                self.email.text = FIRAuth.auth()?.currentUser?.email

                let imageUrl = String(user.photoUrl)

{
  "riders" : {
    "rider 1" : {
      "email" : "rider1@me.com",
      "password" : "whatever",
      "photoUrl" : "https://firebasestorage.googleapis.com/...",
      "usersname" : "rider 1"
    }
  }
}