To reproduce open HelloHTMLEditor and select new font size

Result
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.scene.web.skin.HTMLEditorSkin$16.changed(HTMLEditorSkin.java:706)
at com.sun.javafx.scene.web.skin.HTMLEditorSkin$16.changed(HTMLEditorSkin.java:702)
at com.sun.javafx.binding.ExpressionHelper$Generic.fireValueChangedEvent(ExpressionHelper.java:347)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(ObjectPropertyBase.java:105)
at javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
at javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:145)
at javafx.scene.control.ComboBoxBase.setValue(ComboBoxBase.java:153)
at javafx.scene.control.ComboBox.updateValue(ComboBox.java:449)
at javafx.scene.control.ComboBox.access$300(ComboBox.java:164)
at javafx.scene.control.ComboBox$6.changed(ComboBox.java:434)