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### What?
Fixes a bug where `afterChange` hooks would attempt to access values for
fields that are `read: false` but `create: true`, resulting in
`undefined` values and unexpected behavior.
### Why?
In scenarios where access control allows field creation (`create: true`)
but disallows reading it (`read: false`), hooks like `afterChange` would
still attempt to operate on `undefined` values from `siblingDoc` or
`previousDoc`, potentially causing errors or skipped logic.
### How?
Adds safe optional chaining and fallback object initialization in
`promise.ts` for:
- `previousDoc[field.name]`
- `siblingDoc[field.name]`
- Group, Array, and Block field traversals
This ensures that these values are treated as empty objects or arrays
where appropriate to prevent runtime errors during traversal or hook
execution.
Fixes https://github.com/payloadcms/payload/issues/12660
---------
Co-authored-by: Niall Bambury <niall.bambury@cuckoo.co>
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