PHP如果存在SESSION但是为null

How I can check in PHP if SESSION exists but is null.

I have really old self made platform, where visitor can log in as "guest", it sets $_SESSION "guest" but it is NULL.

Now I wan't to show some specific content to only registered. If I check isset($_SESSION['guest']), is_null($_SESSION['guest']) or is_null($_SESSION['guest'] === FALSE they all return same.

How I can check if guest session exists but is null?

Try this:

if(isset($_SESSION['guest']) && is_null($_SESSION['guest']))
{
    // your code
}

if($_SESSION['guest'] == "")
{
    // code
}

You can try using empty instead, for example:

session_start();
if(isset($_SESSION['guest']) && !empty($_SESSION['guest'])) {
    //Session is not null or empty
}
else
{
    //Session is null or empty
}