GetComponent usage returns NullReferenceException, not sure why

Hi everyone. I have a powerup in my game called crate. When the player collides with it I'm trying to run a function called MachineGun() in my FireScript that increases the bullet fireFreq. When my player collides with the powerup I'm getting a NullReferenceException and I don't know why.

 GameController.js

 function OnTriggerEnter(col:Collider){
             if(col.gameObject.tag == "Player" && canPickup){
             canPickup = false;
                 GameObject.Find("PlayerPrefab").GetComponent(FireScript).MachineGun(); //error occurs here. My player is called PlayerPrefab, the FireScript is attached to the prefab, and the script contains a MachineGun() 
                 var cloneCrateSound = Instantiate(crateCollectionSnd, transform.position, transform.rotation);
                 var cloneArmsCollected = Instantiate(armsCollected, transform.position, Quaternion.Euler(Vector3(0,180,0)));
                 
                 renderer.enabled = false;
                 yield WaitForSeconds(2);
                 Destroy(cloneCrateSound);
                 Destroy(cloneArmsCollected);
                 Destroy(gameObject);
             ...
             }

In FireScript.js

 function MachineGun(){
     gunType = 1;
     bulletTimer = 10;
 }