See subject.

ComboBox should either reject null in setItems(), or guard against null without failing during layout().

See attached example. The exception should have happened in FXMLLoader.load(), not in javafx.scene.Parent.layout() - or it shouldn't have happened at all.

SEVERE: null
java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.getIndexOfComboBoxValueInItemsList(ComboBoxListViewSkin.java:444)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.updateDisplayNode(ComboBoxListViewSkin.java:392)
at com.sun.javafx.scene.control.skin.ComboBoxListViewSkin.getDisplayNode(ComboBoxListViewSkin.java:229)
at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.updateDisplayArea(ComboBoxBaseSkin.java:125)
at com.sun.javafx.scene.control.skin.ComboBoxBaseSkin.computePrefHeight(ComboBoxBaseSkin.java:180)
at javafx.scene.Parent.prefHeight(Parent.java:879)
at javafx.scene.layout.Region.prefHeight(Region.java:1384)
at javafx.scene.control.Control.computePrefHeight(Control.java:804)
at javafx.scene.Parent.prefHeight(Parent.java:879)
at javafx.scene.control.Control.prefHeight(Control.java:686)
at javafx.scene.layout.Region.computeChildPrefAreaHeight(Region.java:1599)
at javafx.scene.layout.AnchorPane.computeChildHeight(AnchorPane.java:296)
at javafx.scene.layout.AnchorPane.layoutChildren(AnchorPane.java:327)
at javafx.scene.Parent.layout(Parent.java:1018)
at javafx.scene.Scene.layoutDirtyRoots(Scene.java:513)
at javafx.scene.Scene.doLayoutPass(Scene.java:484)
at javafx.scene.Scene.preferredSize(Scene.java:1485)
at javafx.scene.Scene.impl_preferredSize(Scene.java:1512)
at javafx.stage.Window$10.invalidated(Window.java:719)
at javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:127)
at javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:161)
at javafx.stage.Window.setShowing(Window.java:782)
at javafx.stage.Window.show(Window.java:797)
at javafx.stage.Stage.show(Stage.java:229)
at loadfxml.Main.start(Main.java:47)
at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:207)
at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:76)