[FIX] LDAP login of new users overwriting `fname` from all subscriptions (#13203)

packages/rocketchat-lib/server/functions/setRealName.js

@@ -18,7 +18,10 @@ RocketChat._setRealName = function(userId, name) {
 	RocketChat.models.Users.setName(user._id, name);
 	user.name = name;
 
-	RocketChat.models.Subscriptions.updateDirectFNameByName(user.username, name);
+	// if user has no username, there is no need to updated any direct messages (there is none)
+	if (user.username && user.username !== '') {
+		RocketChat.models.Subscriptions.updateDirectFNameByName(user.username, name);
+	}
 
 	if (RocketChat.settings.get('UI_Use_Real_Name') === true) {
 		RocketChat.Notifications.notifyLogged('Users:NameChanged', {