THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Component and Session's meta data must be serializable.
org.apache.wicket.Application#getHeaderContributorListenerCollection() is renamed to #getHeaderContributorListeners()
This way it is consistent with the other #getXyzListeners() methods in Application class
Behavior changes
org.apache.wicket.request.Url#getQueryString WICKET-4664
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