code: def _ensure_bdd100k_subdir(source_dir, dirpath):
      if not os.path.isdir(dirpath):
          relpath = os.path.relpath(dirpath, source_dir)
          _raise_bdd100k_error(
              "Directory '%s' not found within '%s'."
              % (relpath, source_dir)
          )
  
imports: from copy import deepcopy
  import logging
  import os
  import warnings
  import eta.core.serial
  import eta.core.utils
  import fiftyone
  import fiftyone.core.labels
  import fiftyone.core.metadata
  import fiftyone.core.storage
  import fiftyone.utils.data
label_desc: Use image node_id 4 for calling a global function with example usage: _ensure_bdd100k_subdir(source_dir, dirpath) without return types