How to export a Google Slide to a pdf in portrait orientation using App Script?

Question

I know how to export a slide into a pdf using App Script with such a kind of code :

folder.createFile(holderFile.getBlob()).setName(PropertiesService.getScriptProperties().getProperty(diplomenumber) + '.pdf');

but the problem is that the pdf generated is in landscape orientation instead of portrait orientation even if my slide is in portrait orientation.

So I was wondering if there is a solution to get the pdf generated from Google Slides in portrait orientation using App Script.

Thanks for any good advices.