Online PHP editor | output for m9KoC

<?php $action = $_POST['action'] ?? 'default'; echo "Null coalesce with undefined variable: "; var_dump($action); if (isset($_POST['action'])) { $action = $_POST['action']; } else { $action = 'default'; } echo "If with undefined variable: "; var_dump($action); echo "\n"; // ----------------------------------------- $_POST['action'] = 'value'; $action = $_POST['action'] ?? 'default'; echo "Null coalesce with value: "; var_dump($action); $_POST['action'] = 'value'; if (isset($_POST['action'])) { $action = $_POST['action']; } else { $action = 'default'; } echo "If with value: "; var_dump($action); echo "\n"; // ----------------------------------------- $_POST['action'] = null; $action = $_POST['action'] ?? 'default'; echo "Null coalesce with explicit NULL: "; var_dump($action); // ----------------------------------------- $_POST['action'] = null; if (isset($_POST['action'])) { $action = $_POST['action']; } else { $action = 'default'; } echo "If with explicit NULL: "; var_dump($action);