## Description
//<erase this line> Include a brief description of the task or feature to implement and why//
**Desired behavior/Acceptance criteria (returned value,Concerns have been raised about Z18 as the type of Z516's 'argument' key; expected errorin particular, performan instance expectationsof Z18 can be resolved, etc.)**
* ..whereas we wouldn't want resolution to happen inside an error object.
---Based on comments in [[ https://gitlab.wikimedia.org/repos/abstract-wiki/wikifunctions/function-orchestrator/-/merge_requests/15 | this merge request ]] and also a recent voice conversation, **Z39 **appears to be a good candidate for the type of this key. Z516 is only used in a few places, and changing the type of this key from Z18 to Z39 should require only a smallish effort. Z516 has no uses in WikiLambda and none in function-evaluator.
**Remove all the non-applicable tags from the "Tags" field**Desired behavior/Acceptance criteria (returned value, expected error, performance expectations, leave only the tags of the projects/repositories related to this task**etc.)**
* All tests involving Z516 should continue to work (after being modified appropriately).
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## Completion checklist
* [ ] Before closing this task, review one by one the checklist available here: https://www.mediawiki.org/wiki/Abstract_Wikipedia_team/Definition_of_Done#Back-end_Task/Bug_completion_checklist