[Zaimwa9]

Sending a trait with a null value threw ArgumentError: Invalid value type, so getFeatureFlags(user: …, traits: [Trait(key: 'plan', value: null)]) failed before making the request. In Flagsmith, a null trait value deletes the trait, so null is a valid value.

Trait and TraitWithIdentity now accept null in both directions. A null value is sent as "trait_value": null, and a null value in a response parses as null instead of throwing. *.g.dart is unchanged: it already writes trait_value even when it is null.

Tests cover parsing and serialising null for both classes, and assert the identity request body for a null trait. Without the fix, all four new tests fail.

Traits are not persisted in the SDK's flag storage, so no cache changes are needed.

[Zaimwa9]

@themis-blindfold review

[themis-blindfold]

⚖️ Themis review: 🟠 Fix before merge

TL;DR: Null traits now serialise through all request paths, but the public copyWith API still cannot produce a null value. The completed Flutter tests and Dart analysis checks passed.

Area	Score
🎯 Correctness	3/5
🧪 Test coverage	3/5
📐 Code quality	4/5
🚀 Product impact	3/5

🟠 Majors

• lib/src/core/model/trait.dart:58 — copyWith(value: null) retains the old value instead of producing a deletion request.

📝 Walkthrough

• Trait serialisation - accepts and emits an explicit JSON null for deletion.
• Identity evaluation - includes a null trait value in the identity request body.
• Public trait models - copyWith still conflates an omitted value with explicit null.

🧪 How to verify

1. Run flutter test test/core/models/trait_test.dart test/core/models/trait_identity_test.dart.
2. Assert that Trait(key: 'plan', value: 'pro').copyWith(value: null).toJson()['trait_value'] is null.
3. Assert the same behaviour for TraitWithIdentity, then call createTrait with the copied value against a test identity.
4. Run flutter test test/fg/flagsmith_traits_test.dart.
   Automate: add the two copyWith(value: null) regression cases to the model tests.

Product take: This makes trait deletion usable across the SDK’s standard update paths. It is a small but important consistency fix for applications that model trait changes immutably.

🧭 Assumptions & unverified claims

No unverified assumptions or claims.

One last null-shaped pebble remains in the immutable path · reviewed at a37840a

[Zaimwa9]

@themis-blindfold review