I dont know why im getting a null reference exception

My first script makes an array and fills it with objects:

 IEnumerator CreateTerrain () 
     {
         for (int px=0; px<chunkSize; px++)
         {
             for (int pz=0; pz<chunkSize; pz++)
             {
                 float Perlin1 = Mathf.PerlinNoise((px+ transform.position.x) /xScale, heightScale);
                 float Perlin2 = Mathf.PerlinNoise((pz+ transform.position.z) /xScale, heightScale);
                 
                 int x = (int) Mathf.FloorToInt(px + transform.position.x);
                 int height = (int) Mathf.FloorToInt(Perlin1*40*Perlin2);
                 int z = (int) Mathf.FloorToInt(pz + transform.position.z);
                 
                 for (int y=0; y<height; y++)
                 {
                     yield return new WaitForSeconds (1/blocksPerSecond);
                     GameObject currentBlock = GameObject.Instantiate(blocks[0], new Vector3(x, y, z), Quaternion.identity) as GameObject;
                     currentBlock.transform.parent = transform;
                     levelData[x, y, z] = currentBlock;
                 }
             }
         }
         
         foreach (Transform block in transform)
         {
             block.GetComponent<BlockScript>().UpdateSides();
         }
     }

My Script that im getting the error on is:

 public void UpdateSides () 
     {
         levelData = new GameObject[chunkSize, chunkHeight, chunkSize];
         
         levelData = leveldataScript.levelData; *** null reference exception ***
         
         print (levelData.GetLength(0) + " , " + levelData.GetLength(1) + " , " + levelData.GetLength(2));
         
         int x = (int) transform.position.x;
         int y = (int) transform.position.y;
         int z = (int) transform.position.z;
         // it continues.....
 

iv been trying to figure out why im getting the error but i have no idea. The console prints out: 10, 100, 10 which means that the array isnt null. Can anyone help please thank you