message: Fix error when inserting null link in Dictionary
diff: @@ -89,7 +89,8 @@ void ListNotifier::run()
  for (size_t i = 0; i < m_prev_size; ++i) {
  if (m_change.modifications.contains(i))
  continue;
  - if (object_did_change(m_list->get_any(i).get<ObjKey>().value))
  + auto m = m_list->get_any(i);
  + if (!m.is_null() && object_did_change(m.get<ObjKey>().value))
  m_change.modifications.add(i);
  }
  