chore: do not create an empty one. Should fail if not in spec

Author: DomKal11

src/LEGO.AsyncAPI/Models/AsyncApiDocument.cs

@@ -46,7 +46,7 @@ public class AsyncApiDocument : IAsyncApiExtensible, IAsyncApiSerializable
         /// <summary>
         /// REQUIRED. The available channels and messages for the API.
         /// </summary>
-        public IDictionary<string, AsyncApiChannel> Channels { get; set; } = new Dictionary<string, AsyncApiChannel>();
+        public IDictionary<string, AsyncApiChannel> Channels { get; set; }
 
         /// <summary>
         /// an element to hold various schemas for the specification.