Calling setGraphic(new Label("TEST")) on a TitledPane *when it is already displayed* raise the following NPE :

java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.LabeledImpl$1.invalidated(LabeledImpl.java:110)
at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:134)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:79)
at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:102)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:109)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:142)
at javafx.beans.property.ObjectProperty.setValue(ObjectProperty.java:63)
at javafx.scene.control.Labeled.setGraphic(Labeled.java:320)