I get the following when deleting network users as part of a bulk actioin from wp-admin/network/users.php:

Warning: implode(): Invalid arguments passed in /var/www/wp-content/plugins/wp-stream-dev/connectors/users.php on line 324

callback_deleted_users() is trying to implode the return of get_role_labels() for a user, but that user no longer exists so NULL is returned.

I have some other custom stuff going on, but I don't see anywhere that I'm hooked into the user deletion process, so I think this would happen anywhere. Happy to troubleshoot or dig more if needed.

This also results in records that look like this: