Particle emitter object destroys itself

Hi fellows, im trying to create a flamethrower. i made a cube and attached particle renderer,mesh particle emitter,particle animator components on it. and then i attached following script to turn on & off the flamethrower but at some point emitting object i mean the cube destroys itself...

 public class FlameThrower : MonoBehaviour {
 
  public ParticleEmitter emitter;
  void Start () {
  emitter=(ParticleEmitter)GetComponent("ParticleEmitter");
  emitter.emit=false;
  }
  
  // Update is called once per frame
  void Update () {
  if(Input.GetKey("z") && emitter.emit==false)
  {
  emitter.emit=true;
  }
  else
  {
  emitter.emit=false;
  }
  }
 }