Twig filter to make sure a variable is an array

WrapArray.php

<?php
namespace Tremby\Twig\Extension;

use Twig_Extension;
use Twig_SimpleFilter;

/**
 * Filter to leave a variable alone if it's array,
 * pass an empty array if the variable was missing,
 * and wrap anything else in an array.
 */
class WrapArray extends Twig_Extension
{
    public function getName()
    {
        return 'WrapArray';
    }

    public function getFilters()
    {
        return [
            new Twig_SimpleFilter('wrapArray', function ($var) {
                if ($var === null) {
                    return [];
                }
                if (!is_array($var)) {
                    return [$var];
                }
                return $var;
            }),
        ];
    }
}