NullReferenceException: Object reference not set to an instance of an object

I have this particle script, but when I try to activate the RPV void I get this error message

NullReferenceException: Object reference not set to an instance of an object particletrigger.Update () (at Assets/Photon Unity Networking/Resources/NetworkScript/particletrigger.cs:22)

 using UnityEngine;
 using System.Collections;
 
 public class particletrigger : MonoBehaviour {
 
 
     private PhotonView myPhotonView;
     // Use this for initialization
     void Start () {
 
         myPhotonView = GetComponent<PhotonView>();
  
     }
     
     // Update is called once per frame
     public void Update () {
 
         if(Input.GetKeyDown(KeyCode.Space))
             networkView.RPC("DoExploder",RPCMode.All, new object[]{15});
 
         else if (Input.GetKeyDown(KeyCode.Return)){
             this.myPhotonView.RPC("DoExploder", PhotonTargets.All, new object[]{122});
 
         }
     
     
     }
 
     [RPC]
     public void DoExploder(int count){
 
         Debug.Log("Check");
         particleSystem.Emit(count);
 
     }
 }