3d Text update. How its work?

Hello. I have some issuses with update Text value of 3d text object.

For example: I create 3d text, qube and ball. When i trow ball in qube and ball collides with qube i need update text of 3d text to "1". i trying many ways, but unity show 1 error.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class PointTracker : MonoBehaviour {
 
      GameObject PointNum;
      Text TextNum;
 
      int CurrentPoints = 0;
 
     // Use this for initialization
     void Start () {
         PointNum = GameObject.Find("PointNum");
         TextNum = PointNum.GetComponent<Text>();
         UpdatePoints(CurrentPoints);
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     public void UpdatePoints(int addNum)
     {
         CurrentPoints = CurrentPoints + addNum;
         TextNum.text = "" + CurrentPoints;
     }
 }

And its

 TextNum.text = "" + CurrentPoints;

Was creating error

 NullReferenceException: Object reference not set to an instance of an object
 PointTracker.UpdatePoints (Int32 addNum) (at Assets/Scripts/PointTracker.cs:27)

Please, help, what i doing wrong?