How to add a gameobject to a null gameobject

The question may seem confusing but I can't think of another way to ask it about it. So I have a project in cloning TWO DOTS the game. So I am making a grid system and I'm trying to assign the circles as game objects onto each grid. The following script creates the grid.

 using UnityEngine;
 using System.Collections;
 
 public class gridManager : MonoBehaviour
 {
         public int width;
         public int height;
         public GameObject[] prefabArray;
         private infoClass[] gridInfo1D;
         private infoClass[,] gridInfo2D;
         public float circleRad;
         //private circleProperty[] circles;
 
         void Start ()
         {
                 gridInfo1D = Initialize (width * height);
                 gridInfo2D = Converter (gridInfo1D, width, height);
 
                 for (int row = 0; row < gridInfo2D.GetLength(0); row++) {
                         for (int column = 0; column < gridInfo2D.GetLength(1); column++) {
                                 GameObject tempCircle = (GameObject)Instantiate (prefabArray [Random.Range (0, prefabArray.Length)], transform.position, Quaternion.identity);
                                 gridInfo2D [row, column].circle = tempCircle;
                                 gridInfo2D [row, column].SendMessage ("SetPos", new Vector2 (row * circleRad, column * circleRad));
 
                         }
                 }
 
         }
 
         infoClass[] Initialize (int size)
         {
                 infoClass[] array = new infoClass[size];
                 return array;
         }
 
         infoClass[,] Converter (infoClass[] array1D, int width, int height)
         {
                 infoClass[,] array2D = new infoClass[width, height];
                 
                 for (int i=0; i<array1D.Length; i++) {
                         int row = i / width;
                         int column = i % width;
                         array2D [row, column] = array1D [i];
                 }
                 return array2D;
         }
 
 }
 

The next script below is the actual class for the grid.

 using UnityEngine;
 using System.Collections;
 
 public class infoClass : MonoBehaviour
 {
 
 
         public string color;
         public bool occupyCheck;
         public GameObject circle;
 
         void Update ()
         {                
                 if (circle) {
                         occupyCheck = true;        
                         color = circle.tag;
                 } else {
                         occupyCheck = false;        
                 }
         }
 
         void SetPos (Vector2 xy)
         {
                 float x = xy.x;
                 float y = xy.y;
                 circle.transform.position = new Vector3 (x, y);
         }
 }
 

The problem is that when I run the code, it gives me a null reference error when I try to assign tempCircle to circle.

 gridInfo2D [row, column].circle = tempCircle;

I understand when I first initialized the gridInfo2D the circle object doesn't exist yet, but is there a way where I can replace that null with an actual game object later?