docs: def item(self, index: int) -> Optional[Node]:
          """Return item with the index.
  
          If the index is negative number or out of the list, return None.
          """
          if not isinstance(index, int):
              raise TypeError(
                  'Indeces must be integer, not {}'.format(type(index)))
          return self.__nodes[index] if 0 <= index < self.length else None