I am running the example from https://github.com/python-control/python-control/blob/master/examples/kincar-flatsys.py. And I am getting an error message as below,

ValueError Traceback (most recent call last)
in ()
130 # Simulation the open system dynamics with the full input
131 t, y, x = ct.input_output_response(
--> 132 vehicle_flat, T, ud, x0, return_x=True)
133
134 # Plot the open loop system dynamics

2 frames
/usr/local/lib/python3.7/dist-packages/control/timeresp.py in _process_labels(labels, signal, length)
681 # Make sure the signal list is the right length and type
682 if len(labels) != length:
--> 683 raise ValueError("List of %s labels is the wrong length" % signal)
684 elif not all([isinstance(label, str) for label in labels]):
685 raise ValueError("List of %s labels must all be strings" % signal)

ValueError: List of output labels is the wrong length**

The program is running in google Colab environment with python version 3.7.
Your help would be much appreciated.