fix(android): fix bad_optional_access when zIndex changes to undefined with props 2.0

[hannojg]

Summary:

When Android props 2.0 diffs a View where zIndex changes from a value to undefined, HostPlatformViewProps::getDiffProps calls zIndex.value() and throws bad_optional_access:

Screen.Recording.2026-03-31.at.15.22.21.mov

This change emits folly::dynamic(nullptr) when zIndex is cleared instead.

Changelog:

[ANDROID] [FIXED] - Fixed a crash when clearing zIndex with props 2.0 enabled

Test Plan:

Use the repro in packages/rn-tester/js/examples/Playground/RNTesterPlayground.js:

function Playground() {
  const [toggle, setToggle] = React.useState(false);

  return (
    <View style={styles.container}>
      <Button title="Toggle" onPress={() => setToggle(t => !t)} />
      <View
        style={{
          backgroundColor: toggle ? 'blue' : 'red',
          height: 100,
          width: 100,
          position: 'absolute',
          zIndex: toggle ? undefined : 1,
        }}
      />
    </View>
  );
}

1. Enable Android props 2.0:

  override fun enableAccumulatedUpdatesInRawPropsAndroid(): Boolean = true
  override fun enableExclusivePropsUpdateAndroid(): Boolean = true
  override fun enablePropsUpdateReconciliationAndroid(): Boolean = true

2. run RNTester Playground on Android, and press Toggle to switch zIndex between 1 and undefined.

This is with the issue fixed:

Screen_recording_20260331_152017.mp4

[hannojg]

I committed the suggestion, i just want to note that the previous syntax structure is the one that the codegen generator will output (and i tried to conform to that but i guess for the manual implemented props it doesn't have to match!)

[meta-codesync]

@NickGerleman has imported this pull request. If you are a Meta employee, you can view this in D98960669.

[react-native-bot]

This pull request was successfully merged by @hannojg in 93b3735

^{When will my fix make it into a release? | How to file a pick request?}

[meta-codesync]

@NickGerleman merged this pull request in 93b3735.