saveUserIdentity coerces missing username/name to literal "undefined", corrupting VideoConference and CallHistory user references

Description:

When saveUserIdentity receives a partial update (for example, only name), it still coerces optional fields with String(rawName).trim() / String(rawUsername).trim().
If one field is omitted, that omitted field can become the literal string "undefined" in internal variables.

Because change detection is computed from these coerced values, usernameChanged/nameChanged can be incorrectly true even when a field was not provided. Later reference updates use those values and can persist "undefined" into user reference fields in video_conference and call_history.

Steps to reproduce:

1. Create a user with existing call/video references (e.g., make at least one media call/video conference so entries exist in call_history / video_conference).
2. Call POST /api/v1/users.updateOwnBasicInfo with only name in data (omit username), for example:
   {
   "data": {
   "name": "New Display Name"
   }
   }
3. Check updated references in video_conference and/or call_history for that user.

Expected behavior:

Only provided fields should be treated as changed.
A name-only update must not alter username references, and no reference field should ever be written as literal "undefined".

Actual behavior:

Omitted optional fields are coerced to string "undefined", and downstream reference updates can write "undefined" into persisted username/name reference fields in video_conference and call_history.

Server Setup Information:

• Version of Rocket.Chat Server: develop (source-level verification)
• License Type: N/A
• Number of Users: N/A
• Operating System: N/A
• Deployment Method: N/A
• Number of Running Instances: N/A
• DB Replicaset Oplog: N/A
• NodeJS Version: N/A
• MongoDB Version: N/A

Client Setup Information

• Desktop App or Browser Version: N/A (API reproduction)
• Operating System: N/A

Additional context

Relevant code paths:

• apps/meteor/app/lib/server/functions/saveUserIdentity.ts

  • String(rawName).trim() / String(rawUsername).trim()
  • nameChanged / usernameChanged computed from coerced values
  • reference writes in VideoConference.updateUserReferences and CallHistory.updateUserReferences

• packages/rest-typings/src/v1/users/UsersUpdateOwnBasicInfoParamsPOST.ts

  • name and username are independently optional
  • apps/meteor/server/methods/saveUserProfile.ts
  • still calls saveUserIdentity for partial identity updates

Relevant logs:

No server exception is required for this bug; it is a data integrity issue caused by incorrect field coercion/change detection logic.

Start with apps/meteor/app/lib/server/functions/saveUserIdentity.ts, then trace the partial-update call from apps/meteor/server/methods/saveUserProfile.ts and the optional fields in UsersUpdateOwnBasicInfoParamsPOST.ts. Reproduce the name-only POST request and inspect VideoConference.updateUserReferences and CallHistory.updateUserReferences; done means omitted fields are not treated as changed and references contain no literal "undefined".