Page History

...

getComponent().getRequestCycle().find(AjaxRequestTarget.class).ifPresent(target -> target.add(this)); 

...

During migration you should check your old code for places where the AjaxRequestCycle (now an Optional<AjaxRequestTarget>) is compared with null:

if (cycle.find(AjaxRequestTarget.class) == null) {
  // this is *never* executed since #find() always returns an Optional
}

if (cycle.find(AjaxRequestTarget.class) != null) {
  // this is *always* executed since #find() always returns an Optional
}

AjaxFallback** components now use java.util.Optional  

Jira
server ASF JIRA serverId 5aa69414-a9e9-3523-82ec-879b028fb15b key WICKET-6104

...