Wrong logpdf for scaled truncated norm function (TPESampler) about optuna HOT 2 CLOSED

out = _norm_logpdf(x) - _log_gauss_mass(a, b) - np.log(scale)

import numpy as np
from scipy.stats import truncnorm as scipy_truncnorm
from optuna.samplers._tpe import _truncnorm as optuna_truncnorm

print(f"scipy pdf(0, a=-10, b=10, scale=1): {np.exp(scipy_truncnorm.logpdf(0, a=-10, b=10, scale=1))}")
print(f"optuna pdf(0, a=-10, b=10, scale=1): {np.exp(optuna_truncnorm.logpdf(0, a=-10, b=10, scale=1))}")
print("---")
print(f"scipy pdf(0, a=-10, b=10, scale=2): {np.exp(scipy_truncnorm.logpdf(0, a=-10, b=10, scale=2))}")
print(f"optuna pdf(0, a=-10, b=10, scale=2): {np.exp(optuna_truncnorm.logpdf(0, a=-10, b=10, scale=2))}")

scipy pdf(0, a=-10, b=10, scale=1): 0.3989422804014327
optuna pdf(0, a=-10, b=10, scale=1): [0.39894228]
---
scipy pdf(0, a=-10, b=10, scale=2): 0.19947114020071632
optuna pdf(0, a=-10, b=10, scale=2): [0.39894228]