struct User: Codable {
  let firstName: String
  let lastName: String?
}

struct User_D: Decodable {
  let firstName: String
  let lastName: String?

  private enum CodingKeys: CodingKey {
    case firstName
    case lastName
  }

  init(from decoder: any Decoder) throws {
    let container: KeyedDecodingContainer<User_D.CodingKeys> = try decoder.container(keyedBy: User_D.CodingKeys.self)

    self.firstName = try container.decode(String.self, forKey: User_D.CodingKeys.firstName)
    self.lastName = try container.decodeIfPresent(String.self, forKey: User_D.CodingKeys.lastName)

  }
}

struct User_E: Encodable {
  let firstName: String
  let lastName: String?
}