When no handlers are configured the client should not blow up

Source/MQTTnet/Client/MqttClient.cs

@@ -101,7 +101,11 @@ namespace MQTTnet.Client
                 _logger.Info("Connected.");
 
                 Connected?.Invoke(this, new MqttClientConnectedEventArgs(authenticateResult));
-                await ConnectedHandler?.HandleConnectedAsync(new MqttClientConnectedEventArgs(authenticateResult));
+                if(ConnectedHandler != null)
+                {
+                    await ConnectedHandler.HandleConnectedAsync(new MqttClientConnectedEventArgs(authenticateResult));
+                }
+               
 
                 return authenticateResult;
             }
@@ -265,7 +269,10 @@ namespace MQTTnet.Client
 
                 _logger.Info("Disconnected.");
                 Disconnected?.Invoke(this, new MqttClientDisconnectedEventArgs(clientWasConnected, exception));
-                await DisconnectedHandler?.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception));
+                if(DisconnectedHandler != null)
+                {
+                    await DisconnectedHandler.HandleDisconnectedAsync(new MqttClientDisconnectedEventArgs(clientWasConnected, exception));
+                }
             }
         }
 

Tests/MQTTnet.Core.Tests/MqttClientTests.cs

@@ -80,7 +80,7 @@ namespace MQTTnet.Tests
                 await client1.SubscribeAsync("x");
 
                 var receivedValues = new List<int>();
-     
+
                 async Task Handler1(MqttApplicationMessageHandlerContext context)
                 {
                     var value = int.Parse(context.ApplicationMessage.ConvertPayloadToString());
@@ -138,8 +138,8 @@ namespace MQTTnet.Tests
                         replies.Add(context.ApplicationMessage.Topic);
                     }
                 }
-                
-                client2.UseReceivedApplicationMessageHandler((Action<MqttApplicationMessageHandlerContext>) Handler2);
+
+                client2.UseReceivedApplicationMessageHandler((Action<MqttApplicationMessageHandlerContext>)Handler2);
 
                 await Task.Delay(500);
 
@@ -149,7 +149,7 @@ namespace MQTTnet.Tests
 
                 await Task.Delay(500);
 
-                Assert.AreEqual("reply/request/a,reply/request/b,reply/request/c", string.Join("," , replies));
+                Assert.AreEqual("reply/request/a,reply/request/b,reply/request/c", string.Join(",", replies));
             }
         }
 
@@ -260,11 +260,39 @@ namespace MQTTnet.Tests
                 Assert.IsFalse(client1.IsConnected);
 
                 await client1.ReconnectAsync().ConfigureAwait(false);
-                
+
                 await Task.Delay(1000);
 
                 Assert.AreEqual(2, retries);
             }
         }
+
+        [TestMethod]
+        public async Task NoConnectedHandler_Connect_DoesNotThrowException()
+        {
+            using (var testEnvironment = new TestEnvironment())
+            {
+                await testEnvironment.StartServerAsync();
+
+                var client = await testEnvironment.ConnectClientAsync();
+
+                Assert.IsTrue(client.IsConnected);
+            }
+        }
+
+        [TestMethod]
+        public async Task NoDisconnectedHandler_Disconnect_DoesNotThrowException()
+        {
+            using (var testEnvironment = new TestEnvironment())
+            {
+                await testEnvironment.StartServerAsync();
+                var client = await testEnvironment.ConnectClientAsync();
+                Assert.IsTrue(client.IsConnected);
+
+                await client.DisconnectAsync();
+
+                Assert.IsFalse(client.IsConnected);
+            }
+        }
     }
 }