Swift如何知道json key是否为空或无key？

import Foundation

let jsonString = """
{
    "name": "John",
    "age": 30,
    "email": null
}
"""

if let jsonData = jsonString.data(using: .utf8) {
    do {
        if let json = try JSONSerialization.jsonObject(with: jsonData, options: []) as? [String: Any] {
            if let name = json["name"] as? String {
                print("Name: \(name)")
            } else {
                print("Name key is empty or does not exist")
            }
            
            if let age = json["age"] as? Int {
                print("Age: \(age)")
            } else {
                print("Age key is empty or does not exist")
            }
            
            if let email = json["email"] as? String {
                print("Email: \(email)")
            } else {
                print("Email key is empty or does not exist")
            }
        }
    } catch {
        print("Error parsing JSON: \(error)")
    }
}