need help in script

hi,
am doing tic tac toe game. i got stuck with my script where i have a two dimensional array variable in which i store my instantiated prefabs. below is the script. can some one tell me where am i making mistake. need help.

the error what i get is

NullReferenceException: A null value was found where an object instance was required.
collider_spawner.createPattern () (at Assets/scripts/collider_spawner.cs:34)
collider_spawner.Start () (at Assets/scripts/collider_spawner.cs:17)

using UnityEngine;
using System.Collections;

public class collider_spawner : MonoBehaviour {

	public GameObject[,] totalcards;
	public GameObject samplePlane;

	private float xPositionValue = 0.0f;
	private float yPositionValue = 4.71f;



	// Use this for initialization
	void Start () {

		createPattern();	
	}
	
	// Update is called once per frame
	void Update () {
	
	}

	void createPattern()
	{
		for(int i = 0; i < 3; i++)
		{
			for(int j = 0; j < 3; j++)
			{
				//Vector3 card_Prefab_Position = new Vector3((j * 3.60f) + xPositionValue, (-i * 3.72f) + yPositionValue, -0.4f);
				
				//Instantiate(card_Collider_prefab, card_Prefab_Position, Quaternion.identity);
				totalcards[i,j] = (GameObject)Instantiate(samplePlane);

				totalcards[i,j].transform.position = new Vector3((j * 3.60f) + xPositionValue, (-i * 3.72f) + yPositionValue, -0.4f);
			}
			
		}
	}
}

Replace your Start method with the following code, and make sure your samplePlane variable is not null.

// Use this for initialization
void Start () {
    totalCards = new GameObject[3,3];
    createPattern();    
}