code: def is_valid(self, search_space):
          
          if not len(search_space) == 1:
              raise RuntimeError('BatchTuner only supprt one combined-paramreters key.')
          
          for param in search_space:
              param_type = search_space[param][TYPE]
              if not param_type == CHOICE:
                  raise RuntimeError('BatchTuner only supprt one combined-paramreters type is choice.')
              else:
                  if isinstance(search_space[param][VALUE], list):
                      return search_space[param][VALUE]
                  raise RuntimeError('The combined-paramreters value in BatchTuner is not a list.')
          return None
docs: Check the search space is valid: only contains 'choice' type
          
          Parameters
          ----------
          search_space : dict