unity3d c#调用脚本报错 ?报错

using UnityEngine;
using System.Collections;

public class Destorybycontact : MonoBehaviour {
public GameObject explosion;
public GameObject playerexplosion;
public int score1;
private Gamecontrol game;

void start()
{
    GameObject gamecontrolobject = GameObject.FindWithTag("GameController");
    if (gamecontrolobject != null)
    {
        game = gamecontrolobject.GetComponent<Gamecontrol>();
    }
    if(gamecontrolobject == null)
    {
        Debug.Log("can't find 'Gamecontrol' scipt");
    }
}

void OnTriggerEnter(Collider other)
{
    if (other.tag == "boundary")
    { return; }
    Instantiate(explosion, transform.position, transform.rotation);
    if (other.tag == "Player")
    {
        Instantiate(playerexplosion, other.transform.position, other.transform.rotation);
    }
    game.addScore(score1);
    Destroy(other.gameObject);
    Destroy(gameObject);
}

}

报错NullReferenceException: Object reference not set to an instance of an object。显示这个是空值game.addScore(score1);。也不知道为什恶魔，求解