code: def _ScanFileSystem(self, scan_node, base_path_specs):
      
      if not scan_node or not scan_node.path_spec:
        raise errors.SourceScannerError(
            'Invalid or missing file system scan node.')
  
      base_path_specs.append(scan_node.path_spec)
docs: Scans a file system scan node for file systems.
  
      Args:
        scan_node (SourceScanNode): file system scan node.
        base_path_specs (list[PathSpec]): file system base path specifications.
  
      Raises:
        SourceScannerError: if the scan node is invalid.