Fix API Crash

[mfosterw]

And add regression test. I added an assert to silence a mypy error without realizing that the type error wouldn't cause a crash but the assert would.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9d46620) to head (03bb2d1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #318   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         2019      2017    -2     
=========================================
- Hits          2019      2017    -2     

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