This was an issue that arose during refactoring of the Title class. The error below is for historic interest. Since we had a good discussion below about how and why the Parser uses RevisionRecord and Title for "non-existable pages" (pages that not only aren't currently in the database, but *can't* be saved in the database), I'm repurposing this bug to reflect the refactoring tasks discussed below.
MediaWiki version: 1.36.0-wmf.36
Constructing RevisionRecord for a page that can't exist: Special:MyLanguage/Main Page [Called from MediaWiki\Revision\MutableRevisionRecord::__construct]
A few of them immediately after pushing 1.36.0-wmf.36 to group1
They all came from metawiki / wtp* servers and the URL /w/rest.php/meta.wikimedia.org/v3/transform/wikitext/to/lint