got trouble:object reference not set to a instance of an object

 using UnityEngine;
 using System.Collections;
 
 public class shoot : MonoBehaviour {
     public Rigidbody2D bullet;
     public float shoot_interval=0.3f;
     float cur_interval ;
     // Use this for initialization
     void Start () {
         cur_interval = 0;
     }
     
     // Update is called once per frame
     void Update () {
       if (Input.GetKey (KeyCode.H)) {
             cur_interval -= Time.deltaTime;
             if(cur_interval<0){
                 cur_interval = shoot_interval;
                 Rigidbody bul = Instantiate(bullet,transform.position,transform.rotation) as Rigidbody;
                 if(this.GetComponentInParent<playerControl>().faceright==false){
                     //Debug.Log("left");
                     Vector3 vec= new Vector3(-1*transform.localScale.x,transform.localScale.y,transform.localScale.z);
                     bul.transform.localScale = vec;
                 }
                 else{
                     //Debug.Log("right");
                 }
             }    
         }
 
     }
 }

When I press H I want to create a bullet which is a prefab, and I've already drag it to the inspector The error shows up at the line "bul.transform.localScale = vec;" and I don't know why. Any body help? How should I change my code?(the if-else sentence is used to change the direction of the bullet. I can initiate the bullets but can not change the direction of the bullet because of this error.)