Suppose there's a website that lets users upload their own software, like mods in a video game, and their terms of service contain a clause that requires and assumes all uploaded software to be MIT licensed:
XIV. Mods
All mods uploaded into {{site}} must be licensed with the MIT license. Any mods without a license specified are assumed to be licensed by the MIT license.
How does this work if a user uploads software that either:
is not otherwise licensed (e.g., a GitHub repo with no LICENSE file), or
has a conflicting license (say, GPLv3)?
Does uploading the software to the site with such Terms of Service overwrite the license of that version of the software? Concretely, can users other than the host with those Terms of Service then also assume the software (at that version) to be MIT licensed? How much effect do such Terms of Service clauses have? Is there a precedence order between contract law and copyright law?
(I can't find any case law or articles about this on public-access search engines, although that's likely 'cause I haven't mastered this type of search.)