docs: def get_persistent_boot_device(self):
          """Get the current persistent boot device set for the host."""
          result = self._get_persistent_boot()
          boot_mode = self._check_boot_mode(result)
  
          if boot_mode == 'bios':
              return result[0]['value']
  
          value = result[0]['DESCRIPTION']
          if 'HP iLO Virtual USB CD' in value:
              return 'CDROM'
  
          elif 'NIC' in value or 'PXE' in value:
              return 'NETWORK'
  
          elif common.isDisk(value):
              return 'HDD'
  
          else:
              return None