Because that line in itself is valid code - it’s just that awake() is not going to get called by Unity, as Awake() will be. So pajaro was uninitialized when it got to Update(), hence the null reference.
It did not say anything was wrong on that line because there technically is nothing wrong with it. All you did was create a perfectly fine method. Problem is Unity doesn’t call the awake() method, it calls the Awake() method, So the error doesn’t show up until you try to reference the Rigidbody that never got called in awake().