When a new user clicks "edit your subscriptions" without having subscribed to a subverse they will see an error document:
You don't have any subscriptions so we have to show you this instead.
[insert goat here]
Subscribe to a subverse you silly goat.
If they subscribe to a subverse, then unsubscribe from it, then "edit your subscriptions" will show an empty Front Set management page.
From the empty Front Set subscriptions page you can add new subverses by name.
Perhaps the Front Set is being created upon first subscription? If so: Suggest creating an empty Front Set upon clicking the "edit your subscriptions" (or at account creation) rather than showing the nonfunctional error page.
Viewing an empty Front set displays the Default when empty; This is the same behavior as if no subscriptions have been made.
On the other hand, the error document encouraging new users into making some subscriptions may be helpful. In that case, suggest helpful instruction for newbie users on how to make a subscription via a screenshot / gif of the subscribe buttons being clicked. This could also be an opportunity to introduce the user to the "popular" and "active" subverse lists by providing links to them (put the main sidebar on that page, and point to it).
protip: Errors due to PEBKAC can be teachable moments.
P.S. "my subverses" terminology is not consistent with "edit your subscriptions", suggest changing to "edit my subscriptions", and "edit my blocked ...". Shorter and more uniform. Dichotomy of "Me" vs "You" should be avoided in UI when they refer to the same entity to avoid confusing users for whom English is not their mother tongue.