Тимур Покровский

The variable SelfTransform of NewBehaviourScript has not been assigned.
You probably need to assign the SelfTransform variable of the NewBehaviourScript script in the inspector

int dur = 1;

//...

if (angle > 90) {
    dur = -dur;
}
float r = 90f;
float l = -90f;
float angle;
transform.Rotate(0, angle * Time.deltaTime * dur, 0);