[PR #1010/0b73cdac backport][0.26] Fix prompting for multivalue options on config

[patchback[bot]]

This is a backport of PR #1010 as merged into main (0b73cdacf560ceef4d3c3dd8de04f4f9898393e2).

Interactive config generation did not allow to specify no headers.

fixes #1008

Review Checklist:

• [ ] An issue is properly linked. [feature and bugfix only]
• [ ] Tests are present or not feasible.
• [ ] Commits are split in a logical way (not historically).