Merge branch 'master' into feature-with-uri

Build/MQTTnet.nuspec

@@ -23,6 +23,7 @@
 * [MQTTnet.Server] Added interceptor for unsubscriptions.
 * [MQTTnet.AspNetCore] improved compatibility with AspNetCore 3.1
 * [Client] Support WithConnectionUri to configure client (thanks to @PMExtra).
+* [Server] Removed exceptions when user properties are set with MQTT protocol version 3.1
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2020</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags> 

Source/MQTTnet/Formatter/V3/MqttV310DataConverter.cs

@@ -20,11 +20,6 @@ namespace MQTTnet.Formatter.V3
         {
             if (applicationMessage == null) throw new ArgumentNullException(nameof(applicationMessage));
 
-            if (applicationMessage.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             return new MqttPublishPacket
             {
                 Topic = applicationMessage.Topic,
@@ -171,11 +166,6 @@ namespace MQTTnet.Formatter.V3
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            if (options.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             var subscribePacket = new MqttSubscribePacket();
             subscribePacket.TopicFilters.AddRange(options.TopicFilters);
             
@@ -186,11 +176,6 @@ namespace MQTTnet.Formatter.V3
         {
             if (options == null) throw new ArgumentNullException(nameof(options));
 
-            if (options.UserProperties?.Any() == true)
-            {
-                throw new MqttProtocolViolationException("User properties are not supported in MQTT version 3.");
-            }
-
             var unsubscribePacket = new MqttUnsubscribePacket();
             unsubscribePacket.TopicFilters.AddRange(options.TopicFilters);