Cannot preview my Mind Map in the share page.

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Start in lib/private/Files/Type/Detection.php at line 377 and follow its use from apps/files_sharing/templates/public.php line 22 through the files_sharing.sharecontroller.showShare route. Reproduce the public share page with the reported mind map file and inspect why the mimeTypeIcon call reaches substr() with a boolean length. Done means the share page renders without this TypeError.