Hi,
I have created two robots from build-in functions, as following. However, I am not able to get "inertia" matrix for robot which has been created from URDF, and I have received this error:

File "C:\Users\moham\miniconda3\envs\rtb\lib\site-packages\roboticstoolbox\robot\ERobot.py", line 2102, in rne
s[j] = link.v.s
AttributeError: 'NoneType' object has no attribute 's'
#############Code#########################
import roboticstoolbox as rtb
panda = rtb.models.URDF.Panda()
puma = rtb.models.DH.Puma560()

print(puma.inertia(puma.qr))
print(panda.inertia(panda.qr))