code: def GetUnscannedScanNode(self):
      
      root_scan_node = self._scan_nodes.get(self._root_path_spec, None)
      if not root_scan_node or not root_scan_node.scanned:
        return root_scan_node
  
      return root_scan_node.GetUnscannedSubNode()
docs: Retrieves the first unscanned scan node.
  
      Returns:
        SourceScanNode: scan node or None if not available.