protected function validateCombinationOptionsProduct($index, &$combination)
    {
        $options = $this->getSubmitted('product_fields.option');

        if (empty($options)) {
            return null;
        }

        $errors = 0;

        foreach ($options as $field_id => $field) {
            if (!empty($field['required']) && !isset($combination['fields'][$field_id])) {
                $this->setErrorRequired("combination.$index.fields.$field_id", $field['title']);
                $errors++;
            }
        }

        return empty($errors);
    }