Nesting Map in Select Resulting In Paginator "Unstable Sort Order"

So my Paginator pagination query works fine until I append:

select: %{media_item: m, channel: chan}

to:

    from(m in MediaItem,
      join: con in ContentMediaItems,
      on: m.id == con.media_item_id,
      where: is_nil(m.published_at) == false,
      join: chan in assoc(con, :channel),
      where: chan.id == con.channel_id,
      join: org in Org,
      on: m.org_id == org.id,
      where: org.slug == ^org_slug,
      order_by: [{:desc, :published_at}],
      preload: [:mediaitemartifacts],
      select: %{media_item: m, channel: chan}
    )

If I nest the result like that, the cursor will result in a nil value:

# RuntimeError at POST /rest/channel/latest_uploads_media_items

Exception:

    ** (RuntimeError) unstable sort order: nullable columns can't be used as the last term
        (paginator 1.1.0) lib/paginator/ecto/query/asc_nulls_last.ex:8: Paginator.Ecto.Query.AscNullsLast.build_dynamic_filter/1

Is there a way to sidestep this so that I can return a nested result? Here is my paginate():

        %{entries: entries, metadata: metadata} =
          Repo.paginate(
            query,
            include_total_count: true,
            after: after_cursor,
            sort_direction: :desc,
            cursor_fields: [{:inserted_at, :desc}, {:id, :asc}],
            limit: limit
          )