Buildfarm pull request test fails without its reason indicated

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A pull request test (for this PR) keeps failing on buildfarm. Looking at its full log I can't find the reason -- tests seem to be passing. I appreciate if someone could take a look at the full log and spot the cause of the error (once this question is resolved I'll update the question title to describe better).

One thing I have no idea is the section at the very end of the job, 15. Clean up to save disk space on slaves where some errors are recorded that look like from Jenkins.

16:00:01 [xUnit] [ERROR] - Conversion error Error to convert - A file not found
16:00:01 ERROR: Step ‘Publish xUnit test result report’ aborted due to exception: 
16:00:01 org.xml.sax.SAXParseException; lineNumber: 2; columnNumber: 1; Premature end of file.