NULL REFERENCE EXCEPTION,NULL REFERENCE EXCEPTION while accessing child objects unity2D

I have a set of bones which follow the IK CCD solver and I am trying to move the position of the first bone with respect to the last bone using transform. For this I am trying to access the Child Objects of the the main body, but I keep getting NULL REFERENCE EXCEPTION

 public class LevelSnake : MonoBehaviour
 {
     private GameObject outputonlinepngtools;
     private Transform lastbone;
     private Transform boneone;
     // Start is called before the first frame update
     void Start()
     {
         outputonlinepngtools = gameObject ;
         boneone = GameObject.Find("bone_1").GetComponent<Transform>();
     }
 
     // Update is called once per frame
     void Update()
     {
         Transform[] alltransforms = outputonlinepngtools.GetComponentsInChildren<Transform>();
         foreach (Transform t in alltransforms){
           if(t.gameObject.name == "bone_23"){
             lastbone.transform.position = t.gameObject.transform.position ;
           }
           if(t.gameObject.name == "bone_1"){
             //boneone.transform.position = lastbone.transform.position;
             t.gameObject.transform.position = lastbone.transform.position;
           }
         }
     }
 }