Warning: "Undefined array key" in PHP — Best Practices to Fix?

Hi everyone,

am running into a PHP warning that keeps popping up in my project:

Warning: Undefined array key "username" in /var/www/html/login.php on line 23

Here’s a simplified snippet of my code:

<?php
$users = [
    ['username' => 'alice', 'email' => 'alice@example.com'],
    ['username' => 'bob', 'email' => 'bob@example.com']
];

foreach ($users as $user) {
    echo "Logging in user: " . $user['username'] . "<br>";
    echo "Email: " . $user['email'] . "<br>";
    echo "Role: " . $user['role'] . "<br>"; // sometimes this key doesn't exist
}
?>

The warning appears when I try to access $user['role'] because not all arrays have this key.

My questions:

1. What’s the best way to handle undefined array keys in PHP?

2. Should I always use isset() / array_key_exists() or is there a cleaner approach in modern PHP?

3. Any tips for handling optional keys in larger associative arrays or JSON data?

Thanks!