Lexical Upload node `fields` prop type not matching database

Describe the Bug

According to the type of the Lexical upload the fields prop cannot be null. However in practice, it can be. This causes TS errors if you use SerializedUploadNode for type assurance (for example for vitest purposes).

If you follow the reproduction steps and open the example file lexical.ts locally, the lexicalImage object cannot have a property of fields as null, but as we see in the screenshot from the database at the bottom, it does.

We can also see that in the current Payload Lexical upload drawer, we have fields as null with a comment: TODO: fix this.

Link to the code that reproduces this issue

https://github.com/OblikStudio/test-payload/tree/payload-lexical-null-upload-field

Reproduction Steps

1. Clone the reproduction repo: https://github.com/OblikStudio/test-payload/tree/payload-lexical-null-upload-field
2. pnpm docker to start the project
3. Open http://localhost:3000/admin
4. Create a user and log in
5. Open http://localhost:3000/admin/collections/pages
6. Create a new page
7. Add an image to the Lexical Text field and fill the necessary slug field
8. Click "Save"
9. Open the API data: http://localhost:3000/admin/collections/pages/{ID}/api
10. You will see that the upload has a "fields": null, prop

To see the TS error open src/lexical.ts. To fix it, you can comment out fields: null, in the object.

Which area(s) are affected? (Select all that apply)

db: mongodb, plugin: richtext-lexical

Environment Info

Binaries:
  Node: 22.14.0
  npm: 10.9.2
  Yarn: N/A
  pnpm: 10.22.0
Relevant Packages:
  payload: 3.64.0
  next: 15.2.3
  @payloadcms/db-mongodb: 3.64.0
  @payloadcms/email-nodemailer: 3.64.0
  @payloadcms/graphql: 3.64.0
  @payloadcms/next/utilities: 3.64.0
  @payloadcms/payload-cloud: 3.64.0
  @payloadcms/richtext-lexical: 3.64.0
  @payloadcms/translations: 3.64.0
  @payloadcms/ui/shared: 3.64.0
  react: 19.2.0
  react-dom: 19.2.0

Start with packages/richtext-lexical/src/features/upload/server/nodes/UploadNode.tsx and compare its SerializedUploadNode fields type with the null value used in packages/richtext-lexical/src/features/upload/client/drawer/index.tsx. Use the linked reproduction and src/lexical.ts to confirm the TypeScript error and inspect the saved API data. Done means the declared type accurately accepts the persisted upload shape and the reproduction no longer reports a type error.