protected function validateClassProduct()
    {
        $field = 'product_class_id';
        $value = $this->getSubmitted($field);

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

        $label = $this->translation->text('Product class');

        if (!is_numeric($value)) {
            $this->setErrorNumeric($field, $label);
            return false;
        }

        $product_class = $this->product_class->get($value);

        if (empty($product_class)) {
            $this->setErrorUnavailable($field, $label);
            return false;
        }

        $fields = $this->product_class->getFields($value);
        $this->setSubmitted('product_fields', $fields);
        return true;
    }