fix --source

[RuRo]

This PR closes #535.

Please make sure to check for the following items:

• Add unit tests and integration tests where applicable.
• Add a line to the release notes (docs/release_notes.rst) under "Current Development Version".

[RuRo]

@samj1912 any comments for this PR? Also, you mentioned that you could make a new release soon, any progress on that?

Edit: I am assuming, that the CI errors are not related to this PR. I can rebase on top of mater if/when #538 gets merged.

Edit edit: Done.

[RuRo]

Sorry to bother you, but would you mind also releasing this fix right away (or maybe later, but relatively soon) while we're at it? I kind of originally expected to get this merged into 6.1.0. It's a tiny change for a whole new version, but I really want to just bump the version once in my project and be done with this.

Edit: thanks! It was nice working with you. :^)