4-differential wheel control in ROS using Action Graph

hello. I am trying to move a robot using 4-differential wheel in Isaac sim. I set the Action Graph using a script, but the error “Nontype” object has no attribute “is_homogeneous” occurs in the Articulation Controller. Is there any solution for this?

Also, when running the script, the following error also occurs.

However, when I looked at my robot, the articulation root was captured. may i know what is the problem?