[acrites]

Conforms to Beam's MapState.computeIfAbsent contract by returning ReadableStates.immediate(null) when a key was absent and a computed value is inserted.

Added support for keys mapped to null: computes and updates when existing == null per the MapState contract ("or is mapped to null").

Added new unit tests to demonstrate these bugs and added some basic unit tests since none previously existed.

[github-actions]

📋 Review Summary

This PR fixes WindmillMapViaMultimap.computeIfAbsent to conform to the MapState contract by returning null upon inserting a computed value and by treating keys mapped to null as absent. It also adds unit test coverage in WindmillMapViaMultimapTest.

🔍 General Feedback

• The logic in computeIfAbsent is sound and properly replaces existing null entries via put(key, inserted).
• There is an unused import in the new test file that will likely trigger Checkstyle/Spotless failures in CI, as well as a couple of minor cleanups in WindmillMapViaMultimap and WindmillMapViaMultimapTest.

---

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.97%. Comparing base (76f6e6d) to head (1669ffd).
⚠️ Report is 310 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40750       +/-   ##
=============================================
+ Coverage     56.16%   75.97%   +19.80%     
+ Complexity     2288     2273       -15     
=============================================
  Files          1124      259      -865     
  Lines        178336    14377   -163959     
  Branches       1489     1479       -10     
=============================================
- Hits         100170    10923    -89247     
+ Misses        75645     2763    -72882     
+ Partials       2521      691     -1830     

Flag	Coverage Δ
go	?
java	75.97% <ø> (+0.18%)	⬆️
python	?

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[acrites]

/gemini review

[github-actions]

📋 Review Summary

This PR fixes WindmillMapViaMultimap.computeIfAbsent to align with the MapState contract by returning ReadableStates.immediate(null) upon inserting a computed value and handling keys mapped to null. It also introduces a comprehensive unit test suite in WindmillMapViaMultimapTest covering core map operations and edge cases, with all previous review feedback addressed.

🔍 General Feedback

• The implementation in WindmillMapViaMultimap is clean, avoids redundant iterator creation, and properly overwrites null-mapped keys via put(key, inserted).
• The unit test coverage in WindmillMapViaMultimapTest thoroughly validates the contract fixes and standard MapState operations.

---

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[github-actions]

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[damccorm]

R: @scwhittle

[github-actions]

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[scwhittle]

I find it pretty confusing that MapState.computeIfAbsent doesn't match Java Map.computeIfAbsent behavior where it returns the existing or newly computed value. https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#computeIfAbsent-K-java.util.function.Function-

I think it would be better to update the comment and match Map. Especially if the existing implementations are already behaving the other way.