code: def _file_field(*args):
      for axis_def in args:
          if axis_def is not None:
              for file, val in axis_def.items():
                  if isinstance(val, str):
                      yield file, val
                  elif isinstance(val, list):
                      for field in val:
                          yield file, field
  
imports: import os
  from typing import Any, Dict, Iterable, List, Optional, Tuple, Union
  from funcy import first, last
  from dvc.exceptions import DvcException
  from dvc.render import FIELD, FILENAME, INDEX, REVISION
  from .None import Converter
label_desc: Use image node_id 2 for calling a global function with example usage: _file_field() without return types