Index: trunk/src/org/openstreetmap/josm/tools/ImageResource.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/ImageResource.java	(revision 10640)
+++ trunk/src/org/openstreetmap/josm/tools/ImageResource.java	(revision 10642)
@@ -198,4 +198,7 @@
             //Use default Swing functionality to make icon look disabled by applying grayscaling filter.
             Icon disabledIcon = UIManager.getLookAndFeel().getDisabledIcon(null, new ImageIcon(bimg));
+            if (disabledIcon == null) {
+                return null;
+            }
 
             //Convert Icon to ImageIcon with BufferedImage inside