fix: Fix clearing optional view props crashing with "Value is null"

[mfazekas]

Fixes #1184, closes #1189 (the alternative converter-level fix): instead of loosening JSIConverter<std::optional<T>> for all conversions, this maps null to "no value" only for view props - CachedProp::fromRawValue treats null like undefined, unless the prop's type explicitly models null (e.g. string | null). Method arguments and hybrid object properties stay strict about null vs undefined.

For view props that distinction doesn't exist anyway: React sends null both for a removed prop (ReactNativeAttributePayload.js#L390-L394) and for an explicit undefined (#L270-L277), so the native side cannot tell them apart - it just crashed the commit with Exception in HostFunction: <View>.<prop>: Value is null, expected a String.

Also covers optional callback props (not fixed by #1189): those crashed earlier, in the generated { f: ... } unwrap (value.asObject()), before any converter ran.

Notes:

• For props that model null (foo?: string | null), clearing the prop delivers null, not undefined - React's payload makes the two indistinguishable, and null-modeling types take null at face value. Pinned by a test.
• Required props are untouched: a null payload still throws, with the original "Value is null" message.
• The callback-prop part lives in generated code, so libraries pick it up by re-running nitrogen; the CachedProp part ships with react-native-nitro-modules directly.

Tests: optional props on the existing TestView + on-device harness tests in example/__tests__/views.harness.tsx (clearing a prop needs React's commit path, so this can't live in getTests.ts). They fail on main (#1433) and pass here, verified on iOS and Android.

Checklist

• Targets main, narrow scope.
• Test pins the bug: fails on main (test: Add failing tests for clearing optional view props (#1184) #1433), passes with the fix.
• bun specs run, generated files committed.
• bun lint-all passes locally.
• No existing specs or test cases removed, no unrelated refactors.
• Conventional Commits.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
nitro-docs	Skipped		Jul 28, 2026 12:19pm

[mrousavy]

Overall this PR is quite good and fixes a valid bug - thank you!

I will investigate a bit further to see if we can get the prop converter fully into Nitro core so that it's not a burden of the generated code to properly convert props. That includes the f unwrapping of functions, seems like there's more stuff we need to do to support Views than just unwrap props :)