AttributeError: 'Parameter' object has no attribute 'value'

[BlueShit-1120]

When I run mountain_car.py in the examples file, it works fine at the beginning, but after a while it will report an error. The error is

model GP1 is right
Traceback (most recent call last):
File "C:/Users/xxwan/.mujoco/mujoco-py/PILCO-master/examples/mountain_car.py", line 57, in
pilco.optimize_models()
File "c:\users\xxwan\desktop\tendontrack_pilco\pilco\models\pilco.py", line 62, in optimize_models
self.mgpr.optimize(restarts=restarts)
File "c:\users\xxwan\desktop\tendontrack_pilco\pilco\models\mgpr.py", line 89, in optimize
"lengthscales": model.kernel.lengthscales.value(),
AttributeError: 'Parameter' object has no attribute 'value'

How can I solve this problem? Thanks.