How can I solve this error?

my script : public class Move : MonoBehaviour {

 public CharacterController CC;

 public Animator Ani;

 float MoveSpeed;
 float TurnSpeed;

 Vector3 V3;

 // Use this for initialization
 void Start () {

     MoveSpeed = 5f;
     TurnSpeed = 2f;
 
 }
 
 // Update is called once per frame
 void Update () {

     V3 = new Vector3 (0, Input.GetAxis ("Mouse X"), 0);


     transform.Rotate (V3 * TurnSpeed); 

     Ani.SetBool ("walk", false);


     if (Input.GetKey (KeyCode.W)) {

         CC.Move(transform.forward * MoveSpeed * Time.deltaTime);
         Ani.SetBool ("walk", true);

     }

     if (Input.GetKey (KeyCode.A)) {
         
         CC.Move(transform.right * -1f * MoveSpeed * Time.deltaTime);
         Ani.SetBool ("walk", true);

     }

     if (Input.GetKey (KeyCode.S)) {
         
         CC.Move(transform.forward * -1f * MoveSpeed * Time.deltaTime);
         Ani.SetBool ("walk", true);

     }

     if (Input.GetKey (KeyCode.D)) {
         
         CC.Move(transform.right * MoveSpeed * Time.deltaTime);
         Ani.SetBool ("walk", true);

     }
 
 }

}

UnassignedReferenceException: The variable Ani of Move has not been assigned. You probably need to assign the Ani variable of the Move script in the inspector. UnityEngine.Animator.SetBool (System.String name, Boolean value) (at C:/buildslave/unity/build/artifacts/generated/common/modules/AnimatorBindings.gen.cs:270) Move.Update () (at Assets/Scripts/M