Crash when accessing Object properties after decoding from JSON

I have decodes JSON value into object. The object looks as expected, but when I try to access it's property.

let jsonData = try JSONSerialization.data(withJSONObject: JSON, options: [])
let decoder = JSONDecoder()
let doctor = try! decoder.decode(Doctor.self, from: jsonData)
let txt = "\(doctor.title). \(doctor.firstName) \(doctor.lastName)" // Runtime crash: (Thread 1: EXC_BAD_ACCESS (code=1, address=0x40))

Runtime crash: (Thread 1: EXC_BAD_ACCESS (code=1, address=0x40))

Class Person:

import UIKit

class Person: Codable {
    let firstName: String
    let lastName: String
    let imageURL: URL

    private enum CodingKeys: String, CodingKey {
        case firstName
        case lastName
        case imageURL = "profileImgPath"
    }

    init(firstName: String, lastName: String, imageURL:URL) {
        self.firstName = firstName
        self.lastName = lastName
        self.imageURL = imageURL
    }
}

Class Doctor:

import UIKit

class Doctor: Person {
    var title: String


    private enum CodingKeys: String, CodingKey {
        case title
    }

    init(firstName: String, lastName: String, imageURL:URL, title: String) {
        self.title = title
        super.init(firstName: firstName, lastName: lastName, imageURL: imageURL)
    }

    required init(from decoder: Decoder) throws {

        let values = try decoder.container(keyedBy: CodingKeys.self)
        self.title = try values.decode(String.self, forKey: .title)
        try super.init(from: decoder)
    }

}

from Crash when accessing Object properties after decoding from JSON