Index: event.js
===================================================================
--- event.js	(revision 4816)
+++ event.js	(working copy)
@@ -242,6 +242,10 @@
 		// Empty object is for triggered events with no data
 		event = jQuery.event.fix( event || window.event || {} ); 
 
+		// make sure event.type is defined
+		if( !event.type )
+		    event.type = "";
+
 		// Namespaced event handlers
 		var parts = event.type.split(".");
 		event.type = parts[0];