public function jsonSerialize()
    {
        // A vcard does not have sub-components, so we're overriding this
        // method to remove that array element.
        $properties = [];

        foreach ($this->children() as $child) {
            $properties[] = $child->jsonSerialize();
        }

        return [
            strtolower($this->name),
            $properties,
        ];
    }