code: def _ensure_bdd100k_dir(source_dir):
      if source_dir is None:
          _raise_bdd100k_error(
              "You must provide a `source_dir` in order to load the BDD100K "
              "dataset."
          )
  
      if not os.path.isdir(source_dir):
          _raise_bdd100k_error(
              "Source directory '%s' does not exist." % 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 3 for calling a global function with example usage: _ensure_bdd100k_dir(source_dir) without return types