renaming and added cast

Source/MQTTnet/Client/MqttClient.cs

@@ -561,7 +561,7 @@ namespace MQTTnet.Client
                 {
                     await SendAsync(new MqttPingRespPacket(), cancellationToken).ConfigureAwait(false);
                 }
-                else if (packet is MqttDisconnectPacket disc)
+                else if (packet is MqttDisconnectPacket disconnectPacket)
                 {
                     // Also dispatch disconnect to waiting threads to generate a proper exception.
                     _packetDispatcher.Dispatch(packet);
@@ -569,7 +569,7 @@ namespace MQTTnet.Client
                     await DisconnectAsync(new MqttClientDisconnectOptions() 
                     {
                         // todo conversion
-                        ReasonCode = disc.ReasonCode
+                        ReasonCode = (MqttClientDisconnectReason)(disconnectPacket.ReasonCode ?? MqttDisconnectReasonCode.UnspecifiedError)
                     }, cancellationToken).ConfigureAwait(false);
                 }
                 else if (packet is MqttAuthPacket authPacket)

Source/MQTTnet/Server/MqttClientSessionsManager.cs

@@ -391,9 +391,9 @@ namespace MQTTnet.Server
                 _connections.AddOrUpdate(connectPacket.ClientId, key => 
                 {
                     return connection;
-                }, (key, tempexistingConnection) =>
+                }, (key, tempExistingConnection) =>
                 {
-                    existingConnection = tempexistingConnection;
+                    existingConnection = tempExistingConnection;
                     return connection;
                 });