add missing warning about discarded value

[zeitlinger]

All other data types already had this warning

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.17%. Comparing base (de48d1b) to head (a4bc011).
⚠️ Report is 34 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7821   +/-   ##
=========================================
  Coverage     90.16%   90.17%           
- Complexity     7229     7230    +1     
=========================================
  Files           821      821           
  Lines         21809    21811    +2     
  Branches       2136     2137    +1     
=========================================
+ Hits          19665    19667    +2     
  Misses         1472     1472           
  Partials        672      672           

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