Laravel 4 Queued Mailing throws error while directly sending works - php

Question

I have a Laravel 4 app where I need to send certain emails to users. I have no idea why but I keep getting this error on my test server (it does not happen on my local vagrant box)
Argument 1 passed to Illuminate\Mail\Mailer::getQueuedCallable() must
be of the type array, null given, called in
blablabla/vendor/laravel/framework/src/Illuminate/Mail/Mailer.php
on line 238 and defined
I tried resetting everything: database, clean clone from git. None of these worked. I also cleared my browser cache and cookies out of desperation. I am using Sync queue. So it's not even an actual queue.
Mail::send works just fine. Mail::queue throws the error above.
I literally started to pull my hair out so any help will be greatly appreciated.
Here is my code:
This is my BookingMailer class that extends Mailer class.
// partner bir arabanın rezervasyonuna onay verdiğinde müşteriye gönderilecek ödeme linki
public function sendPaymentLinkToCustomer($customer, $partner, $booking) {
$view = 'emails.bookings.request_confirmed';
$data = [
'user' => $customer->full_name // string,
'partner' => $partner->display_name // string,
'reference' => $booking->reference // integer,
'booking_id' => $booking->id // integer
];
return $this->sendTo($customer, 'Booking Request Confirmed', $view, $data, true, true);
}
And this is my Mailer class that actually queues the mail.
public function sendTo($user, $subject, $view, $data = array(), $admin_copy=false, $send_as_pm=false)
{
Mail::queue($view, $data, function ($message) use ($user, $view, $data, $subject, $admin_copy) {
$message = $message->to($user->email)->replyTo(Config::get('mail.from.address'), Config::get('mail.from.name'))->subject($subject);
return $message;
});
}

Answer 1

Here is the solution to this problem (at least in my case)
I was including the user first and last name to the mail. I was only showing the first letter of the last name, though. And I was using substr for a UTF-8 string, and that's why sometimes it returned problematic characters that get inside the data array and ultimately cause the queue to break.
When i used mb_substr instead of substr, my problem disappeared.
Phew, I thought I would never figure this one out on my own.