Object reference not set to an instance of an object

Hello, I'm pretty new to Unity and Java programming and I've been trying to make a score system.

I have a script called ScoreController and it looks like this :

 private var textScore : GUIText;
 public var Score : int;
 var Amount : int;
 
 function Awake()
 
 {
 
     textScore = GameObject.Find("TextScore").GetComponent(GUIText);
     
 }
 
 function Update()
 
 {
 
     textScore.text = "Score: " + Score.ToString();
  
 }
  
 function AddScore()
 
 {
 
     Score++;
 
 }
 
 function SubtractScore()
 
 {
 
     Score--;
 
 }
 
 function SetScore(Amount)
 
 {
 
     Score = Amount;
     
 }

And I'm using enemy object with script CountdownTimer :

 var scoreController : ScoreController;
 public var allowedTime : int = 5;
 private var currentTime = allowedTime;
 
 function Awake()
 
 {
 
     TimerTick();
  
 }
 
 function TimerTick()
 
 {
 
     while(currentTime > 0)
     
     {
 
         yield WaitForSeconds(1);
         currentTime--;
         
     }
     
     scoreController.GetComponent(ScoreController).SubtractScore();
     Destroy (this.gameObject);
     
 }

I want it to wait 5 seconds, subtract score and destroy itself. I also have other script that I found on google. It instantiates objects randomly so they all become clones of a prefab.

 var spawnPoints : Transform[];  // Array of spawn points to be used.
 var enemyPrefabs : GameObject[]; // Array of different Enemies that are used.
 var soundSpawn : AudioClip;
 var amountEnemies = 20;  // Total number of enemies to spawn.
 var yieldTimeMin = 0.5;  // Minimum amount of time before spawning enemies randomly.
 var yieldTimeMax = 1.5;  // Don't exceed this amount of time between spawning enemies randomly.
 var i = 5;
  
 function Start()
 {
     Spawn();
 }
  
 function Spawn() 
 { 
    for (i=0; i<10; i++) // How many enemies to instantiate total.
    {
       yield WaitForSeconds(Random.Range(yieldTimeMin, yieldTimeMax));  // How long to wait before another enemy is instantiated.
  
       var obj : GameObject = enemyPrefabs[Random.Range(0, enemyPrefabs.length)]; // Randomize the different enemies to instantiate.
       var pos: Transform = spawnPoints[Random.Range(0, spawnPoints.length)];  // Randomize the spawnPoints to instantiate enemy at next.
       audio.PlayOneShot(soundSpawn);
  
       Instantiate(obj, pos.position, Quaternion.Euler(75, 0, 0)); 
       
       i=0;
    } 
 }

But whenever I run the game and 5 seconds pass I get the following error and the object doesn't destroy itself

Object reference not set to an instance of an object

This error happens because of this line:

 scoreController.GetComponent(ScoreController).SubtractScore();

I've been looking for how to correct it all over the place, however I was unable to solve it myself so I'm asking help from you guys. Please help.