Fix #355 and make UpdateAsync return a RestInteractionResponse

src/Discord.Net.Rest/Extensions/EntityExtensions.cs

@@ -179,7 +179,7 @@ namespace Discord.Rest
                 var messageModel = new API.Message
                 {
                     IsTextToSpeech = data.TTS,
-                    Content = data.Content,
+                    Content = (data.Content.IsSpecified && data.Content.Value == null) ? Optional<string>.Unspecified : data.Content,
                     Embeds = data.Embeds,
                     AllowedMentions = data.AllowedMentions,
                     Components = data.Components,

src/Discord.Net.WebSocket/Entities/Interaction/MessageComponents/SocketMessageComponent.cs

@@ -155,7 +155,7 @@ namespace Discord.WebSocket
         /// <param name="func">A delegate containing the properties to modify the message with.</param>
         /// <param name="options">The request options for this <see langword="async"/> request.</param>
         /// <returns>A task that represents the asynchronous operation of updating the message.</returns>
-        public async Task UpdateAsync(Action<MessageProperties> func, RequestOptions options = null)
+        public async Task<RestInteractionMessage> UpdateAsync(Action<MessageProperties> func, RequestOptions options = null)
         {
             var args = new MessageProperties();
             func(args);
@@ -236,7 +236,7 @@ namespace Discord.WebSocket
                 }
             }
 
-            await InteractionHelper.SendInteractionResponseAsync(Discord, response, this, Channel, options).ConfigureAwait(false);
+            return await InteractionHelper.SendInteractionResponseAsync(Discord, response, this, Channel, options).ConfigureAwait(false);
 
             lock (_lock)
             {