Fix breaking changes.

Source/MQTTnet.Extensions.ManagedClient/ManagedProcessFailedEventArgs.cs

@@ -0,0 +1,14 @@
+using System;
+
+namespace MQTTnet.Extensions.ManagedClient
+{
+    public class ManagedProcessFailedEventArgs : EventArgs
+    {
+        public ManagedProcessFailedEventArgs(Exception exception)
+        {
+            Exception = exception ?? throw new ArgumentNullException(nameof(exception));
+        }
+
+        public Exception Exception { get; }
+    }
+}

Source/MQTTnet/Server/MqttServer.cs

@@ -146,7 +146,7 @@ namespace MQTTnet.Server
                     return;
                 }
                 
-                _clientSessionsManager.Stop();
+                await _clientSessionsManager.StopAsync().ConfigureAwait(false);
                 
                 _cancellationTokenSource.Cancel(false);