Index: /trunk/src/org/openstreetmap/josm/gui/preferences/shortcut/PrefJPanel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/preferences/shortcut/PrefJPanel.java	(revision 5253)
+++ /trunk/src/org/openstreetmap/josm/gui/preferences/shortcut/PrefJPanel.java	(revision 5254)
@@ -321,5 +321,5 @@
                     if (panel.cbDisable.isSelected()) {
                         sc.setAssignedModifier(-1);
-                    } else if (panel.tfKey.getSelectedItem().equals("")) {
+                    } else if (panel.tfKey.getSelectedItem() == null || panel.tfKey.getSelectedItem().equals("")) {
                         sc.setAssignedModifier(KeyEvent.VK_CANCEL);
                     } else {