NullReferenceException (local rotation)

I'm getting this error: `NullReferenceException: UnityEngine.Transform.get_localRotation()` for this line right here:

 motor.axle.Rotate(Vector3.up * motor.RPM * Time.deltaTime);

The variable motor is this class:

 public class SimMotor {
 
     public bool active = true;
     public string ID = "MA-1";
     public float RPM = 1;
     public float torque = 1;
     public Transform motorBody = null;
     public Transform axle = null;
     public TextMesh systemDisplay = null;
     public SimGear engagedGear;
 
     public Material[] motorMaterials;
 }

So motor.axle is just the actual transform of the axle on the motor. I just want it to rotate but I keep getting that error. Any idea why?

Note: The 'axle' transform has no children.

Another note: It has nothing to do with the axle transform itself, because I get the error no matter what I set as the axle.

Another Another Note: I'm getting the feeling that Unity is weirding out because this only happened after the last update. Every single error I'm getting, I receive three times every frame and it treats it like they are all separate errors (even though I have Collapse on in the Debug log, there's three separate errors and they happen every frame). No idea why this is happening.