In the provided code examples, what are the differences between using isset and empty functions for session variables?

When checking session variables in PHP, it is important to differentiate between using isset and empty functions. isset checks if a variable is set and not null, while empty checks if a variable is set and not empty (i.e., contains a non-falsey value). When dealing with session variables, it is usually more appropriate to use isset to ensure that the variable is set before attempting to access its value.

// Using isset to check if a session variable is set
if(isset($_SESSION['username'])) {
    // Variable is set, do something with it
    echo "Welcome, ".$_SESSION['username'];
} else {
    // Variable is not set
    echo "Please log in";
}