code: def _get_value(obj, key, default=missing):
      
      if "." in key:
          return _get_value_for_keys(obj, key.split("."), default)
      else:
          return _get_value_for_key(obj, key, default)
docs: Slightly-modified version of marshmallow.utils.get_value.
      If a dot-delimited ``key`` is passed and any attribute in the
      path is `None`, return `None`.