Unknown Cause of NullReferenceException?

So I was going through a question I asked awhile ago because I needed a script someone helped me make off of it and found it and was going to use it in my game, but I’m getting a NullReferenceException error.

Here is the error:

NullReferenceException: Object reference not set to an instance of an object
GridCreator.Place () (at Assets/Scripts/GridCreator.cs:27)

My code for the GridCreator.cs is this:
using UnityEngine;
using System.Collections;
using UnityEditor;

public class GridCreator : MonoBehaviour {

	[MenuItem("Grid Creator/Create the Grid (9x13)")]
	static void Place()
	{
		// change these to work for you:
		string prefabName = "AnchorPoint"; // case sensitive
		Vector3 gridSize = new Vector3(9, 1, 13); // ie. (10, 1, 5) will generate 10 cubes in the x direction, 1 in the y, and 5 in the z
		Vector3 offset = new Vector3(1, 1, 1); // size of the cubes - default is (1, 1, 1)
		string newCubeName = "AnchorPoint"; // leave blank for default name eg. "Cube(Clone)"


		GameObject cube = Resources.Load(prefabName, typeof(GameObject)) as GameObject;


		for (int x = 0; x < gridSize.x; ++x)
		{
			for (int y = 0; y < gridSize.y; ++y)
			{
				for (int z = 0; z < gridSize.z; ++z)
				{
					Vector3 pos = new Vector3(x * offset.x, y * offset.y, z * offset.z);
					GameObject go = Instantiate(cube, pos, cube.transform.rotation) as GameObject;

					if (newCubeName != "")
						go.name = newCubeName;
				}
			}
		}
	}
}

I am confused as to why it is suddenly not working when it did last time I used it. Only difference is the prefab I’m using. I was using a cube, now I’m using a sphere, but that shouldn’t matter.

Nevermind, I fixed my issue! Forgot I had to put “/Prefabs/(insert prefab name here)” as the string prefabName.