What happens when a Cookie expires?

I have a Cookie acting as a UUID for a user login. It is set to expire one year after creation. At the moment I ask for the value of that Cookie and it returns the text. If it returns a blank I know that no Cookie exists, so I create one. But…

Once the Cookie expires in a year, is the cookie removed automatically? Does it still exist but now returns blank? Do I need to delete it? Can I create a new Cookie over the top of an existing Cookie (assuming it still exists, but is blank)?

From stackoverflow:

And yes the cookie will be REMOVED and not returned to your server if it’s expired. But you can “Reset” cookie with a longer expiry. Say your cookie expires next week where you want it to be expire after 2 weeks, if you user logs in tomorrow you can then reset the cookie to have a new expiry time of 2 weeks. Then the user has 2 weeks to come back without login again.