"Revert to published" publishes draft values for fields absent from the published document #18671

Describe the Bug

Clicking Revert to published retains and publishes a draft field value when that field was absent from the published document. The public API then returns the draft text.

Reproduced on 3.90.1 with a minimal MongoDB-backed collection, without application hooks or plugins. Existing published text, an explicit empty string, and null revert correctly; an omitted field does not.

Link to the code that reproduces this issue

Minimal configuration and steps are inline below. Affected implementation: Status.performAction.

Reproduction Steps

1. Add this collection:

   {
     slug: 'posts',
     versions: { drafts: { validate: true } },
     fields: [{ name: 'description', type: 'textarea' }],
   }

2. Create a published document with the field omitted

3. Once published empty, enter a description, and Save draft.

4. Revisit the document, click Revert to published, and confirm.

5. Read the published document without draft: true.

Expected: Description remains absent; draft changes are discarded.

Actual: The draft description is now published.

The revert action GETs the published document and PATCHes its JSON back. The absent field is omitted from that request, while the update uses the latest draft as its base, retaining the draft value.

Related: #15976 reports a similar symptom for PostgreSQL upload/relationship fields; this reproduction uses a plain textarea on MongoDB.

Which area(s) are affected?

area: ui, area: core, db: mongodb

Environment Info

payload / @payloadcms/ui / @payloadcms/db-mongodb: 3.90.1
Next.js: 16.3.6
Node.js: 24.19.0 (isolated Local API reproduction: 24.15.0)
macOS, arm64