Fix handling of Union'd iterables

[BrianPugh]

Fixes #780

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.75%. Comparing base (222b85f) to head (fa706ec).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #781   +/-   ##
=======================================
  Coverage   89.75%   89.75%           
=======================================
  Files          71       71           
  Lines        8216     8218    +2     
  Branches     1860     1861    +1     
=======================================
+ Hits         7374     7376    +2     
  Misses        477      477           
  Partials      365      365           

Flag	Coverage Δ
unittests	89.68% <100.00%> (+<0.01%)	⬆️

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