Object reference not set to an instance of an object, How can I fix it?

I follow the tutorial to make a game, and I done exactly with the tutorial. However some errors occur. When the player on trigger the coin, the coin can't destroy and the particle also not occur. How can I fix it. NullReferenceException: Object reference not set to an instance of an object ItemPickup+$OnTriggerEnter$17+$.MoveNext () (at Assets/Scripts/ItemPickup.js:34)

 enum PickupType                                                                
 {
         Grow      = 0,                                                              
     Key       = 1,                                                            
     Coin      = 2,                                                            
     Fireball  = 3,                                                            
     ExtraLife = 4,                                                             
     GameTime  = 5                                                             
 } 
 
 var pickupType               = PickupType.Grow;                                
 var pickupValue              : int              = 1;                         
 var itemParticle             : Transform;                                     
 var soundItemPickup          : AudioClip;                                      
 var soundDelay               : float            = 0.0;                          
 var soundRate                : float            = 0.0;                         
             
 private var playerGameObject : GameObject;                                       
 private var hudGameObject    : GameObject;                                       
 private var extraLifeEnabled : boolean          = false;                        
 
 function Start()                                                                 
 {
     playerGameObject = GameObject.FindWithTag("Player");                         
     hudGameObject    = GameObject.FindWithTag("hud");                            
 }
 function OnTriggerEnter(other : Collider)                                           
 {
     if ( other.tag == "collisionBoxBody" )                                         
     {
            var pProp = playerGameObject.GetComponent(PlayerProperties);
         
         ApplyPickup( pProp );
         
         renderer.enabled = false;
         
         if (itemParticle)
         {
             Instantiate(itemParticle, transform.position, transform.rotation);
         }
         if (soundItemPickup)
         {
             PlaySound (soundItemPickup, 0);
         }
         yield WaitForSeconds(audio.clip.length);
         if (extraLifeEnabled)
         {
             pProp.lives += pickupValue;
             extraLifeEnabled = false;
         }
         Destroy (other.gameObject);
     }
 }
 function ApplyPickup(playerStatus : PlayerProperties)                  
 {
     var hudConnect = hudGameObject.GetComponent(HudController);        
     
     switch (pickupType)                                                
     {
         case PickupType.Grow:                                          
             if (playerStatus.playerState != PlayerState.MarioFire)    
             {
                 playerStatus.playerState = PlayerState.MarioLarge;     
                 playerStatus.changeMario = true;                       
             }
             break;
         case PickupType.Key:                                           
             playerStatus.AddKeys (pickupValue);                        
             break;
         case PickupType.Coin:                                         
             playerStatus.AddCoin (pickupValue);                        
             hudConnect.coin += pickupValue;                            
             break;
         case PickupType.Fireball:                                      
             playerStatus.playerState =     PlayerState.MarioFire;         
             playerStatus.hasFire = true;                               
             playerStatus.changeMario = true;                           
             break;
         case PickupType.ExtraLife:                                     
             extraLifeEnabled = true;                                   
             break;
         case PickupType.GameTime:                                      
             // playerStatus.AddTime(pickupValue);                      
             break;
     }
 }
 function PlaySound(soundName : AudioClip, soundDelay : float)
 {
     if (!audio.isPlaying && Time.time > soundRate)
     {
         soundRate = Time.time + soundDelay;
         audio.clip = soundName;
         audio.Play();
     }
 }