Access renderer from transform

Hi guys,

I have been trying to access the Renderer from a Transform that I have instantiated. The error is "Object reference not set to an instance of an object", and it appeared at the GridEnable and GridDisable functions, where I called the tile.gameObject.renderer.enabled.

This is the GridScript, which control the grid in a 2D plane:

 using UnityEngine;
 using System.Collections;
 
 public class GridScript : MonoBehaviour {
     
     public int gridWidth = 9;
     public int gridHeight = 9;
 
     public int remainingGrid;
     public int totalGrid;
     
     public Transform[,] grid;
     public int[,] gridStatus;
     public int[,] gridBorder;
     
     private PlayerControl playerControl;
     
     // Use this for initialization
     void Awake ()
     {
         playerControl = GameObject.FindWithTag ("Player").GetComponent<PlayerControl>();
     }
     
     public void GridEnable(Transform tile)
     {
         tile.gameObject.renderer.enabled = true;
         int x = Mathf.RoundToInt (tile.localPosition.x);
         int y = Mathf.RoundToInt (tile.localPosition.y);
         gridStatus [x, y] = 0;
     }
 
     public void GridDisable(Transform tile)
     {
         tile.gameObject.renderer.enabled = false;
         int x = Mathf.RoundToInt (tile.localPosition.x);
         int y = Mathf.RoundToInt (tile.localPosition.y);
         gridStatus [x, y] = 1;
     }
     }

And This is the GridSetup, which used to generate the grid from a text file

 using UnityEngine;
 using System.Collections;
 
 public class GridSetup : MonoBehaviour {
 
     public int gridHeight = 9;
     public int gridWidth = 9;
     public Transform normalTile;
     public TextAsset textFile;
 
     private GridScript gridScript;
     private string text;
 
     // Use this for initialization
     void Awake () {
         gridScript = GetComponent<GridScript>();
         text = textFile.text;
         CreateGrid (text, gridScript);
     }
 
     // Translate a text file into a map of grid, store in gridScript
     void CreateGrid (string text, GridScript gridScript) {
 
         // Initialize the grid
         gridScript.gridHeight = gridHeight;
         gridScript.gridWidth = gridWidth;
         gridScript.grid = new Transform[gridWidth + 2, gridHeight + 2];
         gridScript.gridStatus = new int[gridWidth + 2, gridHeight + 2];
         gridScript.gridBorder = new int[gridWidth + 2, gridHeight + 2];
         gridScript.totalGrid = gridHeight * gridWidth;
 
         int xx = 0;
         int yy = gridHeight;
         foreach (char c in text) 
         {
             if (c == '\r') continue;
             if (c == '\n') {
                 xx = 0;
                 yy--;
             }
             else {
                 xx++;
                 gridScript.grid[xx, yy] = 
                     Instantiate(normalTile, new Vector3((float)xx, (float)yy, 8f), Quaternion.identity) as Transform;
                 if (c == 'x') {
                     gridScript.GridDisable(gridScript.grid[xx, yy]);
                     gridScript.totalGrid--;
                 }
                 else
                 {
                     gridScript.GridEnable(gridScript.grid[xx, yy]);
                 }
             }
         }
 
         gridScript.remainingGrid = gridScript.totalGrid;
     }
 }