use proper name fallback

Author: sampaiodiego

apps/meteor/server/services/room/service.ts

@@ -326,7 +326,8 @@ export class RoomService extends ServiceClassInternal implements IRoomService {
 			...(inviter && { inviter: { _id: inviter._id, username: inviter.username!, ...(inviter.name && { name: inviter.name }) } }),
 			...autoTranslateConfig,
 			...getDefaultSubscriptionPref(userToBeAdded),
-			...(room.t === 'd' && inviter && { fname: inviter.name, name: inviter.username }),
+			// `name` is optional for users, so fall back to the username like `getNameForDMs` does
+			...(room.t === 'd' && inviter && { fname: inviter.name || inviter.username, name: inviter.username }),
 		});
 
 		if (insertedId) {

ee/packages/federation-matrix/src/helpers/getOrCreateFederatedUser.ts

@@ -11,8 +11,8 @@ const logger = new Logger('federation-matrix:user');
 
 /**
  * `name` is deliberately not required: Rocket.Chat users are valid with a username and no
- * display name (`Accounts_RequireNameForSignUp` off), and every consumer falls back to the
- * username, so demanding it would drop membership events for nameless local users.
+ * display name (`Accounts_RequireNameForSignUp` off), so demanding it would drop membership
+ * events for nameless local users. Consumers must fall back to the username when displaying.
  */
 type FederatedUser = RequiredField<IUser, 'username'>;