Unity Car Tutorial Error

Hello, I followed the Unity Car Tutorial but got an error:

NullReferenceException: Object reference not set to an instance of an object Car.CalculateState () (at Assets/Scripts/JavaScripts/Car.js:502) Car.FixedUpdate () (at Assets/Scripts/JavaScripts/Car.js:105)

And This One:

NullReferenceException: Object reference not set to an instance of an object Car.UpdateWheelGraphics (Vector3 relativeVelocity) (at Assets/Scripts/JavaScripts/Car.js:323) Car.Update () (at Assets/Scripts/JavaScripts/Car.js:95)

The actual seems to work fine but my model does not.

Thank you for your time, --JagyCorp