Remove unknown activities from feed.

lib/pleroma/web/ostatus/activity_representer.ex

@@ -22,4 +22,6 @@ defmodule Pleroma.Web.OStatus.ActivityRepresenter do
       {:updated, h.(updated_at)}
     ] ++ attachments
   end
+
+  def to_simple_form(_,_), do: nil
 end

lib/pleroma/web/ostatus/feed_representer.ex

@@ -11,6 +11,7 @@ defmodule Pleroma.Web.OStatus.FeedRepresenter do
     entries = Enum.map(activities, fn(activity) ->
       {:entry, ActivityRepresenter.to_simple_form(activity, user)}
     end)
+    |> Enum.filter(fn ({_, form}) -> form end)
 
     [{
       :feed, [

lib/pleroma/web/websub/websub.ex

@@ -1,6 +1,5 @@
 defmodule Pleroma.Web.Websub do
   alias Pleroma.Repo
-  alias Pleroma.Websub
   alias Pleroma.Web.Websub.WebsubServerSubscription
   alias Pleroma.Web.OStatus.FeedRepresenter
   alias Pleroma.Web.OStatus