         {
             var nRequests:int = 0;
             for each (var responder:ListItemResponder in pendingResponders)
-                nRequests += 1;
+            {
+                if (responder)
+                    nRequests += 1;
+            }
             s += " length=" + length + ", " + nRequests + " pending requests";
         }
         else

        const r:Array = new Array();
        var index:int = 0;
        for each (var item:* in a)
            r[index++] = item;
        return r;
    }
    

    private function deleteAllPendingResponders():void
    {
        for each (var responder:ListItemResponder in pendingResponders)
        {
            if (responder)
                responder.index = -1;
        }
        pendingResponders.length = 0;
    }

