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

I am getting a null reference exception error in my multiplayer FPS, when I am trying to send the character to a spawnpoint after pressing "spawn."

The code starts like this:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class MultiplayerManager : MonoBehaviour
 {

Then it calls the spawnpoints:

 public bool MatchLoaded;
     public MPPlayer MyPlayer;
     public GameObject[] Spawnpoint = new GameObject[4];
     
     void Start()
     {
         instance = this;
         PlayerName = PlayerPrefs.GetString("PlayerName");
         CurrentMap = MapList[0];
         DontDestroyOnLoad(gameObject);
     }

Then the server and client spawning systems:

 [RPC]
     void Server_SpawnPlayer(NetworkPlayer player)
     {
         int numberspawn = Random.Range(0, Spawnpoint.Length - 1);
         networkView.RPC("Client_SpawnPlayer", RPCMode.All, player, Spawnpoint[numberspawn].transform.position + new Vector3(0, 2, 0), Spawnpoint[numberspawn].transform.rotation);
     }
     
     [RPC]
     void Client_SpawnPlayer(NetworkPlayer player, Vector3 position, Quaternion rotation)
     {
         MultiplayerManager.GetMPPlayer(player).PlayerIsAlive = true;
         MultiplayerManager.GetMPPlayer(player).PlayerHealth = 100;
         if (player == MyPlayer.PlayerNetwork)
         {
             MyPlayer.PlayerManager.ControllerTransform.position = position;
             MyPlayer.PlayerManager.ControllerTransform.rotation = rotation;
             MyPlayer.PlayerManager.networkView.RPC("Client_PlayerAlive", RPCMode.All);
         }
         else
         {
             
         }
     }

and the actual button:

 void SpawnMenu()
     {
         if(GUI.Button(new Rect(5, Screen.height - 40, 250, 35), "Spawn"))
         {
             if (Network.isServer)
                 Server_SpawnPlayer(Network.player);
             else
                 networkView.RPC("Server_SpawnPlayer", RPCMode.Server, Network.player);
         }
     }

Thank you in advance for any and all help! This is a very frustrating issue. If you need more code (for reference) then ask and I will try to get back to you.