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

@@ -65,7 +65,10 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.ArticleNotePageValidator do
   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(%{"replies" => %{"first" => first}} = data) do

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

@@ -146,4 +146,17 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.ArticleNotePageValidatorTest
                "<span class=\"h-card\"><a class=\"u-url mention\" data-user=\"#{local_user.id}\" href=\"#{local_user.ap_id}\" rel=\"ugc\">@<span>akkoma_user</span></a></span>"
     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