NadekoBot.Extensions should now be fully annotated with nullable reference types as well as many classes from NadekoBot.Common

src/NadekoBot/Common/Collections/ConcurrentHashSet.cs

@@ -1,4 +1,5 @@
-// License MIT
+#nullable disable
+// License MIT
 // Source: https://github.com/i3arnon/ConcurrentHashSet
 
 using System.Diagnostics;
@@ -810,4 +811,4 @@ public sealed class ConcurrentHashSet<T> : IReadOnlyCollection<T>, ICollection<T
             Next = next;
         }
     }
-}
+}