public function getCustomWitnesses($filterIsDue = false)
    {
        $list = collect();

        foreach (config('eyewitness.custom_witnesses', []) as $witness) {
            if ($this->isValidWitness($witness)) {
                $instance = app($witness);
                if ($filterIsDue) {
                    if ($instance->isDue()) {
                        $list->push($instance);
                    }
                } else {
                    $list->push($instance);
                }
            }
        }

        return $list;
    }