Beginning Game Designer: Need Help

I picked up a book on game design for complete beginners called "Introduction to Game Design, Prototyping and Development". Everything was fine until I got to the "Hello World: Your First Program" chapter. I followed all the instructions until it said that I had to drag my c# script onto the main camera. I tried to do this but everytime a message popped up saying "NullReferrenceException: Object refererence not set to an instance of the object" Here's the script if that helps: using UnityEngine;
using System.Collections;

public class HelloWorld:MonoBehaviour {

// Use this for initialization
void Start () {
print ("HelloWorld");
}

// Update is called once per frame
void Update () {

}
}

 

I don't see you referencing any objects in this script. This script works perfectly, as well. What other scripts are in your scene? Because the problem isn't here.

 

This is the only script in my scene

 

Do you have any other objects in the scene with attached scripts?

 

No

 

Thanks for all the information.