code: def _read_field_from_msg(msg: Message, field: str) -> Optional[str]:
      """Read Message header field."""
      value = msg[field]
      if value == "UNKNOWN":
          return None
      return value
  
imports: import os
  import stat
  import textwrap
  from email import message_from_file
  from email.message import Message
  from tempfile import NamedTemporaryFile
  from typing import Optional, List
  from distutils.util import rfc822_escape
  from .None import _normalization, _reqs
  from .extern.packaging.markers import Marker
  from .extern.packaging.requirements import Requirement
  from .extern.packaging.version import Version
  from .warnings import SetuptoolsDeprecationWarning
label_desc: Use image node_id 3 for calling a global function with example usage: _read_field_from_msg(msg, field) and returns: value, None