class_docstr: Result transformer to return an arbitrary value from a result dict
code: def __call__(self, res: dict[str, Any]) -> Any:
      if self.field in res:
          return res[self.field]
      else:
          lgr.debug("rejected by return value configuration: %s", res)
          return None
  
imports: from __future__ import annotations
  import logging
  from collections.abc import Iterable, Iterator
  from os.path import isabs, isdir
  from os.path import join
  from os.path import normpath, relpath
  from typing import Any, Optional
  from datalad.distribution.dataset import Dataset
  from datalad.support.exceptions import CapturedException, CommandError, format_oneline_tb
  from datalad.support.path import robust_abspath
  from datalad.utils import PurePosixPath, ensure_list, path_is_subpath
label_desc: Use image node_id 2 for calling the YieldField obj's underlying member method code with example usage: obj.__call__(res) and returns: res, None