code: def _find_mac_under_heading(command, args, heading):
      """Looks for a MAC address under a heading in a command's output.
  
      The first line of words in the output is searched for the given
      heading. Words at the same word index as the heading in subsequent
      lines are then examined to see if they look like MAC addresses.
      """
      stdout = _get_command_stdout(command, args)
      if stdout is None:
          return None
  
      keywords = stdout.readline().rstrip().split()
      try:
          column_index = keywords.index(heading)
      except ValueError:
          return None
  
      first_local_mac = None
      for line in stdout:
          words = line.rstrip().split()
          try:
              word = words[column_index]
          except IndexError:
              continue
  
          mac = _parse_mac(word)
          if mac is None:
              continue
          if _is_universal(mac):
              return mac
          if first_local_mac is None:
              first_local_mac = mac
  
      return first_local_mac
  
imports: import os
  import sys
  from enum import Enum, _simple_enum
label_desc: Use image node_id 5 for calling a global function with example usage: _find_mac_under_heading(command, args, heading) and returns: first_local_mac, None, None, mac