NullReferenceException: Object reference not set to an instance of an object

I currently have 2 GameObjects inactive and not showing in the game camera window, I want to active these GameObjects when there has been a collision with an object already in the game. I have this code but it doesn’t seem to be working.

using UnityEngine;
using System.Collections;

public class GunPickUP : MonoBehaviour 
{

	public GameObject Weapon1;

	void Start()
	{
		Weapon1 = GameObject.Find ("Weapon1");
	}

	void OnTriggerEnter(Collider other)
	{
		if(other.gameObject.tag == "HellGuns")			
		{
			Weapon1.SetActive(true);
			other.gameObject.SetActive(false);
		}
	}	
}

Check this thread for ideas on how to solve NRE.

My initial guess is that GameObject.Find ("Weapon1"); doesn’t actually find anything.