Attempt enum empty instead of checking against a literal array

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

@@ -66,6 +66,10 @@ defmodule Pleroma.Web.MastodonAPI.InstanceView do
       "shareable_emoji_packs",
       "multifetch",
       "pleroma:api/v1/notifications:include_types_filter",
+      "quote_posting",
+      if !Enum.empty?(Config.get([:instance, :local_bubble], [])) do
+        "bubble_timeline"
+      end,
       "editing",
       if Config.get([:media_proxy, :enabled]) do
         "media_proxy"