whereNotIn query builder - empty array

I have an issue whilst trying to exclude courses which are already stated under another heading. Using the following code i am getting the error

Code:

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near ')
AND `events`.`event_deleted_at` IS NULL
ORDER BY `event_user_valid_to` DESC' at line 6

Code:

$this->data['valid_courses'] = $this->event->join('courses', 'courses.course_id = events.course_id')->join('events_users', 'events.event_id = events_users.event_id')->where('event_user_valid_to <=', $today)->orderBy('event_user_valid_to', 'DESC')->findAll();
        $valid_courses_ids  = array_map(function($n) {return $n['course_id'];}, $this->data['valid_courses']);
        $this->data['cid'] = $valid_courses_ids;
        //$valid_courses_ids = [1, 2, 3];

        $this->data['expired_courses'] = $this->event->join('courses', 'courses.course_id = events.course_id')->join('events_users', 'events.event_id = events_users.event_id')->where('event_user_valid_to >=', $today)->whereNotIn('events.course_id', $valid_courses_ids)->orderBy('event_user_valid_to', 'DESC')->findAll();

As you can see the

Code:

$valid_courses_ids

is empty and creates the error but when not empty it doesn't. Am I supposed to just check for such an occurance or am I right in thinking that this should not be aan issue?

Sorry if this is something that you feel is a waste of time but It seemed qquite unusual to me.

Regards,
Jonsmith1982

If the array is empty, it seems the following SQL that is syntax error would be produced.

PHP Code:

$names = [];
$builder->whereNotIn('username', $names);
// Produces: WHERE username NOT IN () 


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