add: merging tinfoilhat json files fails

See https://git.ostc-eu.org/oss-compliance/mirrors/manifest/-/jobs/63494#L36

• fix problem in the code
• @pmoser patch tinfoilhat.json files in the pipeline's a4fpool

@pianon --> I will do this as soon as I have fixed another issue with add and the new command interface... probably already today afternoon