From 3576c4868060edf63233c72aa4db5ccdf1cedd4a Mon Sep 17 00:00:00 2001
From: RogueException <rogueexception@gmail.com>
Date: Sat, 8 Oct 2016 14:47:01 -0300
Subject: [PATCH] Added null check to AsyncEvent

---
 src/Discord.Net.Core/Utils/AsyncEvent.cs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/Discord.Net.Core/Utils/AsyncEvent.cs b/src/Discord.Net.Core/Utils/AsyncEvent.cs
index 0a4d55ed7..a7fdeddf2 100644
--- a/src/Discord.Net.Core/Utils/AsyncEvent.cs
+++ b/src/Discord.Net.Core/Utils/AsyncEvent.cs
@@ -6,6 +6,7 @@ using System.Threading.Tasks;
 namespace Discord
 {
     internal class AsyncEvent<T>
+        where T : class
     {
         private readonly object _subLock = new object();
         internal ImmutableArray<T> _subscriptions;
@@ -19,11 +20,13 @@ namespace Discord
 
         public void Add(T subscriber)
         {
+            Preconditions.NotNull(subscriber, nameof(subscriber));
             lock (_subLock)
                 _subscriptions = _subscriptions.Add(subscriber);
         }
         public void Remove(T subscriber)
         {
+            Preconditions.NotNull(subscriber, nameof(subscriber));
             lock (_subLock)
                 _subscriptions = _subscriptions.Remove(subscriber);
         }