notification_view.ex: Make sure `account` isn’t empty

Related: https://git.pleroma.social/pleroma/pleroma/issues/1203

lib/pleroma/web/mastodon_api/views/notification_view.ex

@@ -25,11 +25,12 @@ def render("show.json", %{
     parent_activity = Activity.get_create_by_object_ap_id(activity.data["object"])
     mastodon_type = Activity.mastodon_notification_type(activity)
 
+    with %{id: _} = account <- AccountView.render("account.json", %{user: actor, for: user}) do
       response = %{
         id: to_string(notification.id),
         type: mastodon_type,
         created_at: CommonAPI.Utils.to_masto_date(notification.inserted_at),
-      account: AccountView.render("account.json", %{user: actor, for: user}),
+        account: account,
         pleroma: %{
           is_seen: notification.seen
         }
@@ -60,5 +61,8 @@ def render("show.json", %{
         _ ->
           nil
       end
+    else
+      _ -> nil
+    end
   end
 end

test/web/mastodon_api/views/notification_view_test.exs

@@ -100,5 +100,11 @@ test "Follow notification" do
       NotificationView.render("index.json", %{notifications: [notification], for: followed})
 
     assert [expected] == result
+
+    User.perform(:delete, follower)
+    notification = Notification |> Repo.one() |> Repo.preload(:activity)
+
+    assert [] ==
+             NotificationView.render("index.json", %{notifications: [notification], for: followed})
   end
 end