Wicket : Change an AjaxSelfUpdatingTimerBehavior

NextReports Server supports an automatic refresh for widgets. Just clicking "Edit Settings" for one widget will bring the following dialog:

Here user can modify "Refresh Time" which tells how many seconds should pass till next auto refresh.

To make this happen , an AjaxSelfUpdatingTimerBehavior is used. By default there is no refresh time set (value is 0). A change will imply to stop previous  AjaxSelfUpdatingTimerBehavior and to create a new one if that's the case:

for (Behavior behavior : widgetPanel.getBehaviors()) {
   if (behavior instanceof AjaxSelfUpdatingTimerBehavior) {
       ((AjaxSelfUpdatingTimerBehavior) behavior).stop();                    
   }
}           
if (refreshTime > 0) {
   widgetPanel.add(new AjaxSelfUpdatingTimerBehavior(Duration.seconds(refreshTime)));
} 

There are two things to have in mind:

1. AjaxSelfUpdatingTimerBehavior must not be removed because, after stop, the event is called one more time on the client, so it has to be present.
2. When we already have a refresh time set (greater than 0) and we want to modify its value, if a refresh is done when the dialog is opened, the desired panel no longer exists. So the user will be informed about this through a message (otherwise an error would have been raised):