Fix import error

Author: nabenabe0928

package/samplers/user_prior_cmaes/sampler.py

@@ -2,6 +2,7 @@
 
 import math
 from typing import Any
+from typing import Union
 
 import cmaes
 import numpy as np
@@ -12,11 +13,13 @@
 from optuna.distributions import IntDistribution
 from optuna.samplers import BaseSampler
 from optuna.samplers import CmaEsSampler
-from optuna.samplers._cmaes import CmaClass
 from optuna.study import StudyDirection
 from optuna.trial import FrozenTrial
 
 
+CmaClass = Union[cmaes.CMA, cmaes.SepCMA, cmaes.CMAwM]
+
+
 class UserPriorCmaEsSampler(CmaEsSampler):
     """A sampler using `cmaes <https://github.com/CyberAgentAILab/cmaes>`__ as the backend with user prior.