code: def _traverse_free_list(
      self,
  ) -> Tuple[Optional[FreelistNode], Optional[FreelistNode]]:
      if self._freelist_start_page == 0:
          return None, None
  
      second_to_last_node = None
      last_node = self.get_node(self._freelist_start_page)
  
      while last_node.next_page is not None:
          second_to_last_node = last_node
          last_node = self.get_node(second_to_last_node.next_page)
  
      return second_to_last_node, last_node
  
imports: import enum
  import io
  from logging import getLogger
  import os
  import platform
  from typing import Union, Tuple, Optional
  import cachetools
  import rwlock
  from .node import Node, FreelistNode
  from .const import ENDIAN, PAGE_REFERENCE_BYTES, OTHERS_BYTES, TreeConf, FRAME_TYPE_BYTES
label_desc: Use image node_id 9 for calling the FileMemory obj's underlying member method code with example usage: obj._traverse_free_list() and returns: second_to_last_node,  last_node, None,  None