Diagrams are displayed as XML in exported documents

Reported by jackdroido on Gitub:

Hi !

I've installed your extension in a personal XWiki installation.

I can draw diagrams and then display them fine using the DIsplay macro (as documented).

But when I try to export the page to PDF, I can only see some XML markup in the document instead of my diagram.

From the App, is not even possible to export the diagram to PNG (the relevant menu entry is grayed out), when on draw.io site is possible.

Is this the expected behaviour ? If not, how can I make the diagram show up in the exported PDF ?

Thanks for your work and time !