TypeError: e is null in console panel

$.ajax({
    type: "POST",
    url: "Rooms.aspx/GetAvailRoom",
    data: '{ Checkin: "' + $checkinDate +
            '", Checkout: "' + $checkoutDate + '" }',
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    success: function (response) {
    var rooms = response.d;
    alert(rooms);
    var html = '';

    if ($.isEmptyObject(rooms)) {
        alert("Room is not Available!")
        var $showError = $('#showError').show().text('We are sorry, there are no rooms available for the dates you have requested.');
        var $showContact = $('#showContact').show().html('If your dates are flexible, please speak to a hotel reservation agent at <strong>+250788400000</strong>.');
        $('#divRooms').hide();
        $('#notificationError').append($showError, '<br/>', $showContact)
        $('div.loading').hide();  
    }
    else if ((rooms == 'undefined') && (rooms == null)) {
        alert("Please go back and choose reservation!");
    }
    else {
        $.each(rooms, function (index, item) {
            $RoomId = item.RoomId;
            html += '<div class="row" data-id=' + item.RoomId + '>';
            html += '<div class="col-md-4">';
            
            html += BxSlider(item);
            html += '</div>';
            html += '<div class="col-md-4">';
            html += '<h3 class="roomname success">' + item.RoomName + '</h3>';
            html += '<p class="price"><em> ' + item.RoomPrice + '$</em> per night</p>';
            html += '<span class="amentiesHeader">Full Description</span>';
            html += '</div>';
            html += '<div class="col-md-4">';
            html += '<div class="roomextra">';

            if (item.RoomDescription != null) {
                html += '<p class="notetitle">' + item.RoomDescription + '</p>';
            }
    
            html += '<button type="button" class="btn btn-success btn-block book" data-id=' + $RoomId + '>BOOK NOW</button>';
            html += '</div>';
            html += '</div>';
            html += '</div>';
        });
    }
        
        $('#divRooms').html(html);
        $('#divRooms div.row').each(function () {
            var RoomID = $(this).attr("data-id");
            var pagerid = '#pager_' + RoomID;

            $(this).find('ul.bxslider').bxSlider({
                pagerCustom: pagerid,
                controls: false       
            });
        });

        $('div.loading').hide();
        $('.book').on("click", function () {
            alert($RoomId);
            var url = "confirm-your-stay.aspx?checkin=" + encodeURIComponent($checkinDate) + "&checkout=" +
            encodeURIComponent($checkoutDate) + "&roomId=" + encodeURIComponent($RoomId) + "&adults=" + encodeURIComponent($adults)
            + "&children=" + encodeURIComponent($children);
            window.location.href = url;
        });
        
        $("#loading").hide();
    }
});