Space Shooter error message

please show us the C# code

I have the same problem((( But did all by tutorial. Asteroids are't getting destroyed also. error text: NullReferenceException: Object reference not set to an instance of an object DestroyByContact.OnTriggerEnter (UnityEngine.Collider other) (at Assets/Scripts/DestroyByContact.cs:33)

And code of DestroyByContact:

using UnityEngine;

using System.Collections;

public class DestroyByContact : $$anonymous$$onoBehaviour { public GameObject explosion; public GameObject playerExplosion; public int scoreValue; private GameController gameController;

 void Start()
 {
     GameObject gameControllerObject = GameObject.FindWithTag ("GameController");
     if (gameControllerObject != null) {
         gameController = gameControllerObject.GetComponent <GameController>();
     }
     if (gameController == null) {
         Debug.Log ("Cannot find 'GameController' script");
     }
 }

 void OnTriggerEnter(Collider other)
 {
     if(other.tag == "Boundary")
     {
         return;
     }
     if(other.tag == "Player")
     {
         Instantiate(playerExplosion, other.transform.position, other.transform.rotation);
     }
     Instantiate(explosion, transform.position, transform.rotation);
     gameController.AddScore (scoreValue);
     Destroy(other.gameObject);
     Destroy(gameObject);
 }

}

And code of GameController:

using UnityEngine; using System.Collections;

public class GameController : $$anonymous$$onoBehaviour { public GameObject hazard; public Vector3 spawnValues; public int hazardCount; public float spawnWait, startWait, waveWait;

 public GUIText scoreText;
 private int score;



 IEnumerator SpawnWaves()
 {
     yield return new WaitForSeconds(startWait);
     while(true)
     {
         for(int i = 0; i < hazardCount; i++)
         {
             Vector3 spawnPosition = new Vector3(Random.Range(-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
             Quaternion spawnRotation = Quaternion.identity;
             Instantiate(hazard, spawnPosition, spawnRotation);
             yield return new WaitForSeconds(spawnWait);
         }
         yield return new WaitForSeconds(waveWait);
     }
 }
 void Start()
 {
     score = 0;
     UpdateScore ();
     StartCoroutine(SpawnWaves());
 }

 public void AddScore (int newScoreValue)
 {
     score += newScoreValue;
     UpdateScore ();
 }
 void UpdateScore()
 {
     scoreText.text = "Score: " + score;
 }

}

Please, Help)) Peace!