Optional fields

<?php
require 'examples/boot.php';

use Cognesy\Instructor\StructuredOutput;

class UserDetail
{
    public int $age;
    public string $firstName;
    public ?string $lastName;
}

$user = StructuredOutput::using('openai')
    ->withMessages('Jason is 25 years old.')
    ->withResponseClass(UserDetail::class)
    ->get();

dump($user);

assert(!isset($user->lastName) || $user->lastName === '');
?>