docs: def _ensure_insert(self, new_items, insert_to):
          """Ensure an item is inserted to a list or create a new empty list
  
          :param new_items: the item(s) to insert
          :type new_items: list(obj)
          :param insert_to: the list on which to insert the items at index 0
          :type insert_to: list()
          """
          insert_to = insert_to or []
          insert_to.insert(0, new_items)
          return insert_to