Can't cast Data from NSKeyedUnarchiver to Object

I archive object to data and save it to disk success by NSKeyedArchiver, but when I get data from NSKeyedUnarchiver, I can't cast it to type Object. I try to do it in many ways, but none of them success. I hope you can help me to solve this problem.. here is my code:

class Person:

class Person: NSObject, NSCoding {
    func encode(with coder: NSCoder) {
        coder.encode(firstName, forKey: "fisrtName")
        coder.encode(lastName, forKey: "lastName")
        coder.encode(age, forKey: "age")
    }

    required convenience init?(coder: NSCoder) {
        guard let firstName = coder.decodeObject(forKey: "firstName") as? String,
            let lastName = coder.decodeObject(forKey: "lastName") as? String else {
                return nil
        }

        let age = coder.decodeInteger(forKey: "age")
        self.init(firstname: firstName, lastName: lastName, age: age)
    }

    let firstName: String
    let lastName: String
    let age: Int

    init(firstname: String, lastName: String, age: Int) {
        self.firstName = firstname
        self.lastName = lastName
        self.age = age
    }
}

Save data to disk:

let tuan = Person(firstname: "Tuan", lastName: "Hoang", age: 21)

            let directoryPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
            let path = directoryPath.first!.appendingPathComponent("PersonData")
            let savePath = path.appendingPathComponent("data.plist")
            do {
                try FileManager.default.createDirectory(at: path, withIntermediateDirectories: true, attributes: nil)

                let data = try! NSKeyedArchiver.archivedData(withRootObject: tuan, requiringSecureCoding: false)

                do {
                    try data.write(to: savePath)
                    print("Save data success")
                } catch {
                    print("Cant save data to path + \(error.localizedDescription)")
                }

            } catch {
                print("Cant not create directory + \(error.localizedDescription)")
            }

Load data:

    do {
                let savedData = try Data.init(contentsOf: savePath)
                print("Get data success")

                guard let data = try? NSKeyedUnarchiver.unarchivedObject(ofClass: Person.self, from: savedData) else {
                    print("Cant cast data")
                    return
                }
                print(data?.firstName)

            } catch {
                print("Cant get saved data ")
            }

your error is here:

    coder.encode(firstName, forKey: "fisrtName")

typo -> firstName