laravel undefined offset 1 - php artisan

I'm running into the following error

Undefined offset: 1

 Open: /home/vagrant/nomad/apps/immixcms/namespace/Cms/Site.php

Laravels debugging displays the following code block

     */
    public static function env($site)
    {
        $cname = 'site_env';

        if(!\Session::has($cname)) {
            $artisan = __DIR__ . "/../../../$site/artisan";
            $env = explode(': ', exec("php $artisan env"))[1];
            \Session::put($cname, $env);
        }

it seems the error is happening on the following line

        $env = explode(': ', exec("php $artisan env"))[1];