What are the potential pitfalls of using isset() to check if a variable is set in PHP and how can they be avoided?

The potential pitfall of using isset() to check if a variable is set in PHP is that it returns true even if the variable is set to null. To avoid this issue, you can use the strict comparison operator (===) to check if a variable is set and not null.

// Potential pitfall: isset() returns true even if variable is set to null
$var = null;
if (isset($var)) {
    echo '$var is set';
} else {
    echo '$var is not set';
}

// Using strict comparison to check if variable is set and not null
if ($var !== null) {
    echo '$var is set and not null';
} else {
    echo '$var is not set or is null';
}