Error in Saving Lidar Point Cloud #56

Hi...
I am try to run the " 07-save-lidar-point-cloud.py ", but it gives me the following:

Python API Quickstart #7: Saving a point cloud from the Lidar sensor
Traceback (most recent call last):
File "./07-save-lidar-point-cloud.py", line 32, in
s.save("lidar.pcd")
File "/home/amr/Downloads/PythonAPI/lgsvl/utils.py", line 23, in new_f
return f(*args, **kwargs)
File "/home/amr/Downloads/PythonAPI/lgsvl/sensor.py", line 105, in save
"path": path,
File "/home/amr/Downloads/PythonAPI/lgsvl/remote.py", line 69, in command
raise Exception(data["error"])
Exception: Object reference not set to an instance of an object

So, what is the problem?! and How to solve it?