I just added a list of children to a group node and got the exception below. While the exception is right that something is indeed wrong, the exception is not accurate. What I added was a list of children containing null values, as in [null, null, someElement, null, null], so the only duplicate elements added was the null-values themselves. In this case, I recommend throwing a new NullChildrenNotAllowedException which would be easier to debug.



java.lang.IllegalArgumentException: Children: duplicate children added: parent = Showcase$2@7287812
at javafx.scene.Parent$1.onProposedChange(Parent.java:307)
at com.sun.javafx.collections.VetoableObservableList.addAll(VetoableObservableList.java:106)
at com.sun.javafx.collections.ObservableListWrapper.addAll(ObservableListWrapper.java:160)
at com.intuism.ui.component.showcase.SlotConstructionTask$3.run(SlotConstructionTask.java:139)
at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:76)