Uncaught TypeError: Cannot convert null to object (ext-all-debug.js:67570)

Code:
onPageMapClear: function() {
        var me = this,
            loadingFlag = me.wasLoading,
            reqs = me.pageRequests,
            req,
            page;

        // If any requests return, we no longer respond to them.
        if (me.data.events.pageadded) {
            me.data.events.pageadded.clearListeners();
        }

        // If the page cache gets cleared it's because a full reload is in progress.
        // Setting the loading flag prevents linked Views from displaying the empty text
        // during a load... we don't know whether ther dataset is empty or not.
        me.loading = true;
        me.totalCount = 0;

        // Cancel all outstanding requests
        for (page in reqs) {
            if (reqs.hasOwnProperty(page)) {
                req = reqs[page];
                delete reqs[page]; //delete req
                delete req.callback; //trying to delete req.callback     

            }
        }

        // This will update any views. 
        me.fireEvent('clear', me);

        // Restore loading flag. The beforeload event could still veto the process.
        // The flag does not get set for real until we pass the beforeload event.
        me.loading = loadingFlag;
    },