Question Object reference not set to instance of an object

I am creating a prototype i set animator controller.

when i press "s" "Bool get true" it plays animation at the end of animation an event is called to make bool false.

But when i press "S" second time it gives Object reference not set to an instance of object and animation does not get played. I know the error is very basic but i am still getting trouble to clear it.
Following are my code scripts:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class DandaAnimations : MonoBehaviour
6. {
7.     Animator animator;
8.     // Start is called before the first frame update
9.     void Start()
10.     {
11.         animator = this.GetComponent<Animator>();
12.     }
13.  
14.     // Update is called once per frame
15.     void Update()
16.     {
17.        
18.     }
19.     public void HitDown()
20.     {
21.         animator.SetBool("hitDown", true);
22.     }
23.     public void Strike()
24.     {
25.         animator.SetBool("dandaSway", true);
26.     }
27.     public void TurnDownFalse()
28.     {
29.         animator.SetBool("hitDown", false);
30.     }
31.     public void TurnStrikeFalse()
32.     {
33.         animator.SetBool("dandaSway", false);
34.     }
35. }
36.  

Controller Script:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class DandaControler : DandaAnimations
6. {
7.     DandaAnimations dandaAnimations;
8.     DandaAnimations currentAction;
9.     GameObject danda;
10.     Animator d_animator;
11.     // Start is called before the first frame update
12.     void Start()
13.     {
14.         d_animator = GetComponent<Animator>();
15.         dandaAnimations = this.gameObject.GetComponent<DandaAnimations>();
16.     }
17.     // Update is called once per frame
18.     void Update()
19.     {
20.         PullGulliUp();
21.     }
22.     void PullGulliUp()
23.     {
24.         if (Input.GetKeyDown(KeyCode.S))
25.         {
26.             dandaAnimations.HitDown();
27.         }
28.         if (Input.GetKeyUp(KeyCode.S))
29.         {
30.             dandaAnimations.TurnDownFalse();
31.         }
32.     }
33. }
34.