RNE method not working for ERobot

[vkzimmerman]

Describe the bug
I am running into a bug where I am trying to use the rne() function on an inherited ERobot and am getting an error "TypeError: list indices must be integers or slices, not NoneType".

Version information
roboticstoolbox-python version 1.1.1
spatialmath-python version 1.1.13

To Reproduce
Steps to reproduce the behavior:
robot2 = rtb.models.DH.Panda()
print(robot2.rne(q=np.array([-1.64904312,-0.10738241,0.0,0.,0.,0.,0.]),qd=np.array([0.,0.,0.,0.,0.,0.,0.]),qdd=np.array([0.,0.,0.,0.,0.,0.,0.]),gravity=np.array([9.81,0.,0.])))
robot3 = rtb.models.ETS.Panda()
print(robot3.rne(q=np.array([-1.64904312,-0.10738241,0.0,0.,0.,0.,0.]),qd=np.array([0.,0.,0.,0.,0.,0.,0.]),qdd=np.array([0.,0.,0.,0.,0.,0.,0.]),gravity=np.array([9.81,0.,0.])))
robot = rtb.models.URDF.Panda()
print(robot.rne(q=np.array([-1.64904312,-0.10738241,0.0,0.,0.,0.,0.]),qd=np.array([0.,0.,0.,0.,0.,0.,0.]),qdd=np.array([0.,0.,0.,0.,0.,0.,0.]),gravity=np.array([9.81,0.,0.])))

Expected behavior
The expected behavior for the example ERobot rne call should be the same result as the rne call with the DH robot. The code runs an example DH robot, ETS robot, and a URDF Erobot. All three return different results. The ERobot especially causes a code breaking error message which is shown in the screenshot below.

Screenshots

Environment (please complete the following information):
-WSL
-Python 3.10.12

Additional context
Add any other context about the problem here.