Null ReferenceException: Object reference not set to an instance of an object

I'm currently working on skills, where my character spawn shield. Then suddenly i get null reference, it was working a while ago. Here's the script:

 private Animator myAnimator;
     private MayariControls controls;
     private Shoot mShoot;
 
     public List<Skill> skills;
 
 
     // Use this for initialization
     void Awake () 
     {
         myAnimator = GetComponent<Animator> ();
         controls = GetComponent<MayariControls>();
         mShoot = GameObject.FindGameObjectWithTag ("Sphere").GetComponent <Shoot>();
     }
     
     // Update is called once per frame
     void FixedUpdate () 
     {
         if (Input.GetKeyDown (KeyCode.Alpha1)) 
         {
 
             if(skills[0].currentCd >= skills[0].cooldown)
             {
                 myAnimator.SetBool ("isShield", true);
                 mShoot.enabled = false;
                 controls.cancelMovement = false;
                 controls.orb.SetActive (true);
                 StartCoroutine(CreateShield());
                 skills[0].currentCd = 0;
 
             }
         } 

the error is in line "mshoot.enable = false"