THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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CheckingObjectOutputStream accepts a list of org.apache.wicket.core.util.objects.checker.IObjectChecker objects which are used to check for different kind of problems during object serialization. Commit diff: d0441059e0
org/apache/wicket/markup/html/border/BoxBorder is removed with no replacement WICKET-4966.
BoxBorder class has been deprecated in Wicket 6.x series