It’s fine that it’s empty. But by setting disabled you’ve made it impossible for users to chose a different theme. That’s also the reason why the winter theme is now gone because you’ve set it as your theme in your account preferences. That setting is now ignored.
Instead of disabling themes entirely you should update your preferences
There you can set a default, that is used for everyone, unless they change it for their own account themselves.
This default will be used at least once when some logs in for the first time.