Fix proto serializer

[jack-berg]

Fixes #8143.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.29%. Comparing base (e8920e7) to head (5a814f5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #8147   +/-   ##
=========================================
  Coverage     90.29%   90.29%           
  Complexity     7649     7649           
=========================================
  Files           843      843           
  Lines         23059    23059           
  Branches       2309     2309           
=========================================
  Hits          20822    20822           
  Misses         1518     1518           
  Partials        719      719           

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