docs: def _validate_args(self, args):
          ''' validate the user arguments '''
          assert(args.bucket)
  
          if args.subscribers:
              for _subscriber in args.subscribers:
                  assert(isinstance(_subscriber, AsperaBaseSubscriber))
  
          if (args.transfer_config):
              assert(isinstance(args.transfer_config, AsperaConfig))
  
              # number of sessions requested cant be greater than max ascps
              if args.transfer_config.multi_session > self._config.ascp_max_concurrent:
                  raise ValueError("Max sessions is %d" % self._config.ascp_max_concurrent)
  
          for _pair in args.file_pair_list:
              if not _pair.key or not _pair.fileobj:
                  raise ValueError("Invalid file pair")