Problems with submitting BatchAndOutput tasks

[gollux]

I have problems with submitting BatchAndOutput tasks via the API.

I am trying to submit one or more output files without a source file and without choosing an explicit language (there is none). CMS rejects the submission with Invalid submission format! - Please select the correct files. in the log. The problem is that match_files_and_language finds multiple candidate languages.

CWS sidesteps the problem by always sending a concrete language even if there are only output files submitted.

We can probably ignore the problem for this IOI, because it's going to have a single language enabled, which avoids the problem. But we should fix it before the next release.