public function addCategory($category)
    {
        if ($category instanceof FeedItemCategory) {
            $this->categories[] = $category;
        } elseif (is_array($category)) {
            if (!empty($category)) {
                $this->categories[] = FeedItemCategory::createFromArray($category);
            }
        } else {
            throw new \InvalidArgumentException('Invalid category');
        }

        return $this;
    }