fix: Treat null as undefined for removed optional View props

[mrousavy]

• Fixes Error when assigning undefined to optional view property #1184

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Summary

• React's Fabric diff sends an explicit null sentinel for a removed prop (ReactNativeAttributePayload: "Flag the leaf property for removal by sending a sentinel") - and prop={undefined} takes the same path, so the two are indistinguishable on the wire
• CachedProp previously passed that null straight into conversion, which throws mid-commit for every optional prop type that rejects null (optional<double> via asNumber(), and hybridRef even earlier, in the { f } function-prop unwrap)
• now: if the prop type is optional and null is not a valid value for it (JSIConverter<T>::canConvert), the value is normalized to undefined → the native setter is called once with nullopt

Semantics

• optional prop removed / set to undefined → setter receives nullopt (the JS-visible value becomes undefined). The native initializer default still only covers never-provided props - a richer "reset on clear" belongs in the implementation (storage ?? default)
• props that can legitimately hold null (NullType, variants containing null): untouched - null stays data, so removal collapses to "explicit null" for those (inherent to React's sentinel protocol)
• required props: unchanged, removal still throws loudly with the ViewName.propName: prefix

Because normalization only applies where conversion was guaranteed to throw, no currently-working behavior can change.

Overhead

• non-optional props: none - the if constexpr (is_optional<T>) branch compiles out
• optional props: one value.isNull() tag check during Props parsing; the canConvert walk only runs when the value actually is null (i.e. an actual removal)

Testing

New Harness test delivers undefined when an optional prop is removed": mounts TestView with nativeDefaultValue={1}+hybridRef, then removes both - asserts the value reads undefined, the setter fired exactly once more, unrelated setters (isBlue) did not fire, and the previously-crashing hybridRef` removal path survives. Red without the fix (commit-time throw), green with it.

Validated: workspace typecheck, eslint (CI settings), clang-format.

🤖 Generated with Claude Code

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
nitro-docs	Skipped		Aug 21, 2026 10:11am