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

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

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

  private enum CodingKeys: CodingKey {
    case firstName
    case lastName
  }

  func encode(to encoder: any Encoder) throws {
    var container: KeyedEncodingContainer<User_E.CodingKeys> = encoder.container(keyedBy: User_E.CodingKeys.self)

    try container.encode(self.firstName, forKey: User_E.CodingKeys.firstName)
    try container.encodeIfPresent(self.lastName, forKey: User_E.CodingKeys.lastName)
  }
}