Question

can session values be null if they are not set? or should I use isset all the time?

Answer 1

There are many ways of doing this, all OK. For example:

• empty($_SESSION['a']) will return true if the value doesn’t exist or is empty (empty array, zero, empty string, etc)
• isset($_SESSION['a']) will return true if the value exists
• array_key_exists('a', $_SESSION) will also return true if the value exists

You shouldn’t just use $_SESSION['a'] == null, because if a does not exist in the $_SESSION array, you will receive a notice.