An example how this might happen:
1. Upgradepath test is triggered.
2. Between 1) and 3), relengs push updates, or something similar happens.
3. Upgradepath looks at -pending repo and sees no packages.
4. Upgradepath has nothing to report (empty list of CheckDetails), only the TAP header is created automatically.

The question is what we want to do about it. Because it is not an error, but a legitimate use case.

Should the TAP output look different? Should we do something with the resultsdb job, except for just creating and closing it?

The behaviour is IMHO correct. Changing the priority for now, but it can IMHO be safely closed if @kparal @mkrizek agree.

Yeah, I think the current behavior is correct.