the error happens in this part of my code but it works fine in a tutorial i was watching
void Update ()
{
if(target == null)
{
return;
}
Vector3 dir = target.position - transform.position;
Quaternion lookRotation = Quaternion.LookRotation(dir);
Vector3 rotation = Quaternion.Lerp(PartToRotate, lookRotation, Time.deltaTime*trunspeed).eulerAngles;
PartToRotate.rotation = Quaternion.Euler(0f, rotation.y, 0f);
}