Queuing mail with attachData in Laravel 5.1 / OctoberCMS

The following IS working when I use Mail::send

$email = 'my@email.com';
$name = 'My Name';
$invoice = InvoicePdf::generate($invoice_id); // generates PDF as raw data

Mail::send('mail.template', null, function($message) use ($name, $email, $invoice) {

    $message->to($email, $name);
    $message->subject('Thank you for your order!');
    $message->attachData($invoicePdf, 'invoice.pdf', ['mime' => 'application/pdf']);

});

It works fine and an email is generated with the correct PDF attachment.

However, if I change Mail::send to Mail::queue then I receive the following error:

Unable to JSON encode payload. Error code: 5

/var/www/html/october/vendor/laravel/framework/src/Illuminate/Queue/Queue.php line 90

If I take the $message->attachData(); line out then it works even with Mail::queue so it seems like the raw data from the attachment is causing issues with the queue but there's nothing in the relevant October or Laravel docs about how to deal with this.

via Chebli Mohamed