Newly added artifact is titled as "undefined"

Logged in as 422196@mail.muni.cz:

Reproduction steps:

1. Go to https://kafe.fi.muni.cz/auth/lemmafimuni/ and create a new project for Filmový festival FI MU #25 (closed)
2. Fill in whatever fields are necessary and confirm "Create project"
   (maybe some steps are missing here? I had to take another flow due to errors)
3. Go to "Files" section
4. Start adding a film

Expected result: A reasonable user-facing message, or name of the file

Actual result: It gets added as "undefined (undefined)" (or "Undefined (Film)" in Czech)