Issue an error when an argument belongs to multiple groups

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (7c1f680) 98.54% compared to head (c9108da) 98.54%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #139 +/- ## ======================================= Coverage 98.54% 98.54% ======================================= Files 25 25 Lines 1790 1792 +2 ======================================= + Hits 1764 1766 +2 Misses 26 26 ```

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