Ayuda!! me tira este error!! Gracias

NullReferenceException: Object reference not set to an instance of an object
ControlPersonaje.Update () (at Assets/ControlPersonaje.cs:38)
38>>(Hacha.GetComponent<CircleCollider2D>().enabled = false


using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class ControlPersonaje : MonoBehaviour {
Rigidbody2D rgb;
Animator anim;
public float maxVel = 5f;
bool haciaDerecha = true;

public Slider slider;
public Text txt;

public float energy=100;

public int costoGolpeAlAire = 1;
public int costoGolpeAlArbol = 3;
public int premioArbol = 15;


bool enFire1 = false;

ControlArbol ctrArbol=null;
public GameObject Hacha=null;


void Start() {
rgb = GetComponent<Rigidbody2D> ();
anim = GetComponent<Animator> ();
Hacha = GameObject.Find ("/orco/orc_body/orc_R_arm/orc_R_hand/orc_weapon");
}

void Update() {
if (Mathf.Abs (Input.GetAxis ("Fire1")) > 0.01f) {
if (enFire1 == false) {
enFire1 = true;
Hacha.GetComponent<CircleCollider2D>().enabled = false;
anim.SetTrigger ("attack");
if (ctrArbol != null) {
if (ctrArbol.GolpeOrco () ) {
energy += premioArbol;
if (energy > 100)
energy = 100;
}
else {
energy -= costoGolpeAlArbol;
}
}
else {
energy -= costoGolpeAlAire;
}
}
} else {
enFire1 = false;
}

slider.value = energy;
txt.text = energy.ToString ();

}

public void HabilitarTriggerHacha() {
Hacha.GetComponent<CircleCollider2D>().enabled = true;
}

void FixedUpdate() {
float v = Input.GetAxis ("Horizontal");
Vector2 vel = new Vector2 (0, rgb.velocity.y);
v *= maxVel;
vel.x = v;
rgb.velocity = vel;

anim.SetFloat ("speed",vel.x);

if(haciaDerecha && v < 0) {
haciaDerecha = false;
Flip();
}
else if(!haciaDerecha && v>0) {
haciaDerecha = true;
Flip();
}
}

void Flip() {
var s = transform.localScale;
s.x *= -1;
transform.localScale = s;
}

public void SetControlArbol (ControlArbol ctr) {
ctrArbol = ctr;
}
}

 

How to fix a NullReferenceException error

https://forum.unity.com/threads/how-to-fix-a-nullreferenceexception-error.1230297/

Steps to success:
- Identify what is null
- Identify why it is null
- Fix that

 

Gracias por la respuesta!, estoy realizando un curso básico de Unity pero no tengo a quien preguntarle donde me estoy equivocando....sigo sin encontrar como arreglarlo