ArticleNotePageValidator: fix replies fixing

Some software, like GoToSocial, expose replies as ActivityPub
Collections, but do not expose any item array directly in the object,
causing validation to fail via the ObjectID validator. Now, Pleroma will
drop that field in this situation too.

lib/pleroma/web/activity_pub/object_validators/article_note_page_validator.ex

@@ -86,7 +86,10 @@ defp fix_replies(%{"replies" => %{"first" => %{"items" => replies}}} = data)
   defp fix_replies(%{"replies" => %{"items" => replies}} = data) when is_list(replies),
     do: Map.put(data, "replies", replies)
 
-  defp fix_replies(%{"replies" => replies} = data) when is_bitstring(replies),
+  # TODO: Pleroma does not have any support for Collections at the moment.
+  # If the `replies` field is not something the ObjectID validator can handle,
+  # the activity/object would be rejected, which is bad behavior.
+  defp fix_replies(%{"replies" => replies} = data) when not is_list(replies),
     do: Map.drop(data, ["replies"])
 
   defp fix_replies(data), do: data

test/pleroma/web/activity_pub/object_validators/article_note_page_validator_test.exs

@@ -32,4 +32,17 @@ test "a basic note validates", %{note: note} do
       %{valid?: true} = ArticleNotePageValidator.cast_and_validate(note)
     end
   end
+
+  test "a Note without replies/first/items validates" do
+    insert(:user, ap_id: "https://mastodon.social/users/emelie")
+
+    note =
+      "test/fixtures/tesla_mock/status.emelie.json"
+      |> File.read!()
+      |> Jason.decode!()
+      |> pop_in(["replies", "first", "items"])
+      |> elem(1)
+
+    %{valid?: true} = ArticleNotePageValidator.cast_and_validate(note)
+  end
 end