创建具有到期日期的 Cookie

我想用 来创建一个 cookie sessionOnly = False，我明白这样做是有必要设置一个到期日期的。但是，未设置到期日期属性。

// set properties dictionary
NSMutableDictionary *cookieProperties = [NSMutableDictionary dictionary];

// insert all values
[cookieProperties setObject:@"myDomain" forKey:NSHTTPCookieDomain];
[cookieProperties setObject:@"myName" forKey:NSHTTPCookieName];
[cookieProperties setObject:@"/" forKey:NSHTTPCookiePath];
[cookieProperties setObject:@"myValue" forKey:NSHTTPCookieValue];
[cookieProperties setObject:@"FALSE" forKey:NSHTTPCookieDiscard];
[cookieProperties setObject:@"0" forKey:NSHTTPCookieVersion];

// setting expiry date for a month from now
[cookieProperties setObject:[[NSDate date] dateByAddingTimeInterval:2629743] forKey:NSHTTPCookieExpires];

// create a cookie with these properties
NSHTTPCookie *cookie = [NSHTTPCookie cookieWithProperties:cookieProperties];

当我查看cookieProperties价值时，我得到：

{
    Discard = FALSE;
    Domain = myDomain;
    Expires = "2019-10-08 23:43:44 +0000";
    Name = myName;
    Path = "/";
    Value = myValue;
    Version = 0;
}

正如它应该。

但cookie价值是：

<NSHTTPCookie
    version:0
    name:myName
    value:myValue
    expiresDate:'(null)'
    created:'2019-09-08 13:14:46 +0000'
    sessionOnly:TRUE
    domain:mydomain
    partition:none
    sameSite:none
    path:myPath
    isSecure:FALSE
 path:"myPath" isSecure:FALSE>

随着expiresDate:'(null)'和sessionOnly:TRUE。这是为什么？