I'm trying to add Smart Search to one of the SPPB modules we have, and I'm gettting error 500 in browser console.

Steps to reproduce:

1. Create a Smart Search Module
2. Create an SPPB module
3. Using the front-end editor, add the Joomla Module Add-on, then choose the Smart Search module you created

Expected: Smart search module renders correctly.

Actual:

Smart search module is never rendered, and the browser console shows error 500 on the following AJAX call:

Request:

POST /index.php?option=com_sppagebuilder&view=ajax&format=json&callback=addon 500 (Internal Server Error)

Response:

{
    "error": true,
    "code": 0,
    "message": "Call to undefined method Joomla\\CMS\\Document\\JsonDocument::addHeadLink()"
}