Object Reference not set to an instance of an object

Code (csharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class gridManager : MonoBehaviour {
5.  
6.     bool blahblah = false;
7.  
8.     public GameObject[,] world;
9.  
10.     public void addToWorld (int x, int y, string type){
11.         //if the array position is not empty
12.         if (world [x,y] != null) {
13.             GameObject n = (GameObject)Instantiate(Resources.Load(type));
14.             //tell the object where is is
15.             n.transform.position = new Vector2(x*10,y*10);
16.             world [x,y] = n;
17.         }
18.     }
19.  
20.     // Use this for initialization
21.     void Start () {
22.    
23.     }
24.    
25.     // Update is called once per frame
26.     void Update () {
27.         if (blahblah == false) {
28.             addToWorld (2,2,"Test Object");
29.             blahblah = true;
30.         }
31.    
32.     }
33. }
34.  

I assume its not finding the "Test Object" prefab?

What I'm trying to do is Instantiate a prefab with 'guidance' from a grid manager. For now I'm trying to check if the array position is empty. If it is, instantiate the "Test Object" prefab at the given x,y coords (*10, because grid size ofc.) Then put a reference to the game object in the array so I can check if from other objects later, by position in the array (and by extension in the game world.)

Any help would be great.

Halbera.

EDIT:

Code (csharp):

1. NullReferenceException: Object reference not set to an instance of an object
2. gridManager.addToWorld (Int32 x, Int32 y, System.String type) (at Assets/gridManager.cs:12)
3. gridManager.Update () (at Assets/gridManager.cs:28)

 

The full error (particularly the line number) would help. These types of errors are also abstract, but it may help.

Also, not the best at C#, but in line 8, shouldn't it be GameObject[0] rather than [,]?

And, sorry that my mind isn't really able to understand that code at the moment. Good luck!

 

I'm trying to make a 2 dimensional array, I read in the scripting docs that is done using [,]

Thanks anyway.