debinstall #71032 bad output from narval plugin [validation pending]

http://dev.giprecia.fr/testexecution/39546 e.g. ends with:

Action apycot.ldi.upload at step 34876 returned bad output:
- Missing output for changes-filesisinstance(elmt, FilePath)
elmt.type == "debian.changes.uploaded"

prioritynormal
typebug
done in2.5.0
load0.100
load left0.000
closed by#2cac75cc2597 narval plugin: return list of changes files instead of nothing (closes #71032)