fix(document): clean modified subpaths if unsetting map

[vkarpov15]

Fix #15519

Summary

If setting a map to null/undefined, need to clean modified subpaths. Otherwise we have dangling modified paths which cause issues like #15519.

Examples

[Copilot]

Pull Request Overview

This PR ensures that when a Map path is unset (assigned null or undefined), any modified subpaths are also cleared to prevent dangling change records. It adds the cleanup logic in Document.prototype.$set and a new test case verifying this behavior.

• Added cleanModifiedSubpaths call for schema maps when unsetting a path in lib/document.js.
• Introduced a test in test/types.map.test.js for setting then unsetting the same map (GH-15519).

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/document.js	Call cleanModifiedSubpaths for schema.$isSchemaMap when val == null.
test/types.map.test.js	New test "handles setting then unsetting the same map" covering the undefined case.

Comments suppressed due to low confidence (2)

test/types.map.test.js:1368

• Consider adding a similar test case for doc.settings = null to ensure that unsetting the map to null also clears modified subpaths as expected.

    doc.settings = undefined;

lib/document.js:1520

• [nitpick] Add a brief comment explaining why we need to clean modified subpaths for schema maps when unsetting (e.g., to avoid dangling change records), so future maintainers understand the intent.

  } else if (schema.$isSchemaMap && val == null) {