Index: /CKEditor/trunk/_source/core/ui.js
===================================================================
--- /CKEditor/trunk/_source/core/ui.js	(revision 4138)
+++ /CKEditor/trunk/_source/core/ui.js	(revision 4139)
@@ -68,5 +68,5 @@
 		var item	= this._.items[ name ],
 			handler	= item && this._.handlers[ item.type ],
-			command = item.command && this._.editor.getCommand( item.command );
+			command = item && item.command && this._.editor.getCommand( item.command );
 
 		var result = handler && handler.create.apply( this, item.args );