Hey i am getting an error in this code with calling hook on "OnEntitySpawned"

using Oxide.Ext.Discord;
using Oxide.Ext.Discord.Attributes;
using Oxide.Ext.Discord.DiscordObjects;
using System;
using static Oxide.Ext.Discord.DiscordObjects.Embed;

namespace Oxide.Plugins
{
    [Info("Test", "Nealo", 1.0)]
    [Description("Nealos test plugin")]

    public class Test : RustPlugin 
    {
        [DiscordClient] DiscordClient _client;
        private void Loaded() { Discord.CreateClient(this, "token"); }
        private void Unload() { Discord.CloseClient(_client); }
        private void OnEntitySpawned(BaseNetworkable entity)


        {
            if (entity is CargoPlane || entity is BaseHelicopter || entity is CargoShip || entity is CH47Helicopter)
            {
                Channel channel = null;

                _client.DiscordServer.channels.FindAll(findChannel =>
                {
                    if (findChannel.id == "not for you ") channel = findChannel;
                    return true;
                });

       

                

                Author author = new Author
                {
                    name = entity.ShortPrefabName + "Inbound",
                    icon_url = GetUrl(entity)
                };

                Embed embed = new Embed
                {
                    author = author,
                    description = GetText(entity),
                    color = 3447003,
                };

                channel.CreateMessage(_client, embed);




            }
        }
        private string GetUrl(object entity)
        {
            if (entity is CargoPlane) return "https://rustlabs.com/img/items180/supply.signal.png";
            if (entity is BaseHelicopter) return "https://rustlabs.com/img/screenshots/helicopter.png";
            if (entity is CargoShip) return "https://www.corrosionhour.com/wp-content/uploads/2018/10/Screenshot-518.png";
            if (entity is CH47Helicopter) return "https://rustlabs.com/img/screenshots/codelockedhackablecrate.png";
            return null;
        }

        private string GetText(object entity)
        {
            if (entity is CargoPlane) return "Cargo Plane Spawned";
            if (entity is BaseHelicopter) return "Attack Heli Inbound";
            if (entity is CargoShip) return "Cargo Ship Spawned";
            if (entity is CH47Helicopter) return "Chinhook Inbound";
            return null;
        }

    }
}
​

| Failed to call hook 'OnEntitySpawned' on plugin 'Test v1.0.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Test.OnEntitySpawned (BaseNetworkable entity) [0x000b7] in <a7a86b0f264e44db9db59b2888c1ecde>:0 
  at Oxide.Plugins.Test.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0007e] in <a7a86b0f264e44db9db59b2888c1ecde>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

Add some null checks and debug output to things that could potentially be null such as entity, channel, etc.