Support null value of message body.

src/DotNetCore.CAP.Kafka/ITransport.Kafka.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System;
-using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using Confluent.Kafka;

src/DotNetCore.CAP/ICapPublisher.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
+using JetBrains.Annotations;
 
 namespace DotNetCore.CAP
 {
@@ -24,35 +25,35 @@ namespace DotNetCore.CAP
         /// Asynchronous publish an object message.
         /// </summary>
         /// <param name="name">the topic name or exchange router key.</param>
-        /// <param name="contentObj">message body content, that will be serialized.</param>
+        /// <param name="contentObj">message body content, that will be serialized. (can be null)</param>
         /// <param name="callbackName">callback subscriber name</param>
         /// <param name="cancellationToken"></param>
-        Task PublishAsync<T>(string name, T contentObj, string callbackName = null, CancellationToken cancellationToken = default);
+        Task PublishAsync<T>(string name, [CanBeNull] T contentObj, string callbackName = null, CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Asynchronous publish an object message with custom headers
         /// </summary>
         /// <typeparam name="T">content object</typeparam>
         /// <param name="name">the topic name or exchange router key.</param>
-        /// <param name="contentObj">message body content, that will be serialized.</param>
+        /// <param name="contentObj">message body content, that will be serialized. (can be null)</param>
         /// <param name="headers">message additional headers.</param>
         /// <param name="cancellationToken"></param>
-        Task PublishAsync<T>(string name, T contentObj, IDictionary<string, string> headers, CancellationToken cancellationToken = default);
+        Task PublishAsync<T>(string name, [CanBeNull] T contentObj, IDictionary<string, string> headers, CancellationToken cancellationToken = default);
 
         /// <summary>
         /// Publish an object message.
         /// </summary>
         /// <param name="name">the topic name or exchange router key.</param>
-        /// <param name="contentObj">message body content, that will be serialized of json.</param>
+        /// <param name="contentObj">message body content, that will be serialized. (can be null)</param>
         /// <param name="callbackName">callback subscriber name</param>
-        void Publish<T>(string name, T contentObj, string callbackName = null);
+        void Publish<T>(string name, [CanBeNull] T contentObj, string callbackName = null);
 
         /// <summary>
         /// Publish an object message.
         /// </summary>
         /// <param name="name">the topic name or exchange router key.</param>
-        /// <param name="contentObj">message body content, that will be serialized of json.</param>
+        /// <param name="contentObj">message body content, that will be serialized. (can be null)</param>
         /// <param name="headers">message additional headers.</param>
-        void Publish<T>(string name, T contentObj, IDictionary<string, string> headers);
+        void Publish<T>(string name, [CanBeNull] T contentObj, IDictionary<string, string> headers);
     }
 }
\ No newline at end of file

src/DotNetCore.CAP/Messages/Message.cs

 using System;
 using System.Collections.Generic;
+using JetBrains.Annotations;
 
 namespace DotNetCore.CAP.Messages
 {
     public class Message
     {
-        public Message(IDictionary<string, string> headers, object value)
+        public Message(IDictionary<string, string> headers, [CanBeNull] object value)
         {
             Headers = headers ?? throw new ArgumentNullException(nameof(headers));
-            Value = value ?? throw new ArgumentNullException(nameof(value));
+            Value = value;
         }
 
         public IDictionary<string, string> Headers { get; }
 
+        [CanBeNull]
         public object Value { get; }
     }
 

src/DotNetCore.CAP/Messages/TransportMessage.cs

 using System;
 using System.Collections.Generic;
+using JetBrains.Annotations;
 
 namespace DotNetCore.CAP.Messages
 {
@@ -8,10 +9,10 @@ namespace DotNetCore.CAP.Messages
     /// </summary>
     public class TransportMessage
     {
-        public TransportMessage(IDictionary<string, string> headers, byte[] body)
+        public TransportMessage(IDictionary<string, string> headers, [CanBeNull] byte[] body)
         {
             Headers = headers ?? throw new ArgumentNullException(nameof(headers));
-            Body = body ?? throw new ArgumentNullException(nameof(body));
+            Body = body;
         }
 
         /// <summary>
@@ -22,6 +23,7 @@ namespace DotNetCore.CAP.Messages
         /// <summary>
         /// Gets the body object of this message
         /// </summary>
+        [CanBeNull]
         public byte[] Body { get; }
 
         public string GetId()

src/DotNetCore.CAP/Serialization/ISerializer.JsonUtf8.cs

@@ -13,13 +13,18 @@ namespace DotNetCore.CAP.Serialization
     {
         public Task<TransportMessage> SerializeAsync(Message message)
         {
+            if (message.Value == null)
+            {
+                return Task.FromResult(new TransportMessage(message.Headers, null));
+            }
+
             var json = JsonConvert.SerializeObject(message.Value);
             return Task.FromResult(new TransportMessage(message.Headers, Encoding.UTF8.GetBytes(json)));
         }
 
         public Task<Message> DeserializeAsync(TransportMessage transportMessage, Type valueType)
         {
-            if (valueType == null)
+            if (valueType == null || transportMessage.Body == null)
             {
                 return Task.FromResult(new Message(transportMessage.Headers, null));
             }