MissingFieldException

on collision with “Bullet” i want the particle to play (which it does not do with a particle system). i only get one error: MissingFieldException: UnityEngine.ParticleSystem.emit
here is the script that i have tried to make:

 var PE : ParticleSystem;
 
 function Start(){
 
     PE.emit = false;
 }
 
 function OnCollisionEnter(c : Collision){
 
     if(c.transform.tag == "Bullet"){
 
         PE.emit = true;
 
     }
 }
 
 function OnCollisionExit(c : Collision){
 
     if(c.transform.tag == "Bullet"){
 
         PE.emit = false;
    
     }
 }

any help or amendments would great

thanks

PE.Emit(amountOfParticles);