Adding sound to animation: NullReferenceException

I'm trying to add sound queues to an animation clip and I seem to get this: NullReferenceException Sound.Update() (at Assets/Somping Sounds/Scripts/Sound.js:14)

 #pragma strict

 var audio1 : AudioClip;
 var audio2 : AudioClip;
 var audio3 : AudioClip;
 
 function Update ()
 {
     if(Input.GetKeyDown("a"))
     {
         BassHit();
         var BassEvent=new AnimationEvent();
         BassEvent.functionName = "BassHit";
         animation["WalkSync"].clip.AddEvent(BassEvent); // Add the event to an AnimationClip
     }
     if(Input.GetKeyDown("s"))
     {
         audio.PlayOneShot(audio2);
     }
     if(Input.GetKeyDown("d"))
     {
         audio.PlayOneShot(audio3);
     }
 }
 function BassHit()
 {
     audio.PlayOneShot(audio1);
 }
 function SnareHit()
 {
 
 }
 function HiHatHit()
 {
 
 }