fix nullreference when using empty password (fix #4)

UserInterface/Views/BrokerSettings.axaml.cs

@@ -45,7 +45,7 @@ namespace UserInterface.Views
         public void Configure(object sender, RoutedEventArgs args)
         {
             var model = (BrokerSettingsViewModel)this.DataContext;
-            var result = this.client.InvokeAsync(x => x.WriteMqttBrokerSettingsAsync(new MqttSettings() { Host = model.Host, Username = model.Username, Password = model.Password }));
+            var result = this.client.InvokeAsync(x => x.WriteMqttBrokerSettingsAsync(new MqttSettings() { Host = model.Host, Username = model.Username, Password = model.Password ?? "" }));
         }
 
         public async void GetSettings()

hass-workstation-service/Data/ConfigurationService.cs

@@ -226,7 +226,7 @@ namespace hass_workstation_service.Data
                 {
                     Host = settings.Host,
                     Username = settings.Username,
-                    Password = settings.Password
+                    Password = settings.Password ?? ""
                 };
 
                 await JsonSerializer.SerializeAsync(stream, configuredBroker);