Remove unknown activities from feed.

lib/pleroma/web/ostatus/activity_representer.ex

@@ -22,4 +22,6 @@ def to_simple_form(%{data: %{"object" => %{"type" => "Note"}}} = activity, user)
       {:updated, h.(updated_at)}
     ] ++ attachments
   end
+
+  def to_simple_form(_,_), do: nil
 end

lib/pleroma/web/ostatus/feed_representer.ex

@@ -11,6 +11,7 @@ def to_simple_form(user, activities, users) 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

 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

test/web/ostatus/activity_representer_test.exs

@@ -2,7 +2,7 @@ defmodule Pleroma.Web.OStatus.ActivityRepresenterTest do
   use Pleroma.DataCase
 
   alias Pleroma.Web.OStatus.ActivityRepresenter
-  alias Pleroma.User
+  alias Pleroma.{User, Activity}
 
   import Pleroma.Factory
 
@@ -32,6 +32,11 @@ test "a note activity" do
     assert clean(res) == clean(expected)
   end
 
+  test "an unknown activity" do
+    tuple = ActivityRepresenter.to_simple_form(%Activity{}, nil)
+    assert is_nil(tuple)
+  end
+
   defp clean(string) do
     String.replace(string, ~r/\s/, "")
   end