Resolve "MultiversePlotCreator DAG support does not allow path-only field specification"

This MR addresses the bug described in #138 (closed) and adds corresponding test code.

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped
  • Reviewed & approved by @herdeanu

Related issues

Closes #138 (closed)