Fix skipping fields with union of unsupported type

[AllanChain]

Fixes #721

The unformatted files are not touched in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.81%. Comparing base (f09d503) to head (f28c811).
⚠️ Report is 56 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #722      +/-   ##
==========================================
- Coverage   90.83%   90.81%   -0.02%     
==========================================
  Files          13       13              
  Lines        2040     2308     +268     
  Branches      370      450      +80     
==========================================
+ Hits         1853     2096     +243     
- Misses        124      141      +17     
- Partials       63       71       +8     

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[yukinarit]

LGTM, thanks!