[AC72] harden macro parser against malicious or falsified input

[clouless]

Bug

We had some strange runtime invocation errors in production in the parser of the macro.
The errors seam to indicate falsified or malicious input to the macro and produce edge cases that should not occur in production.

Acceptance Criteria

• ✅ hardened the parser to only work on strings (object, function input is sanitized) (even though this should never happen anyways)
• ✅ hardened the parser to work with falsified configs (null keys, null values, trees of unknown objects) (even though this should never happen anyways)