Highcharts: Custom property on data point

HTML

<script src="http://highcharts.com/js/testing.js"></script>
<div id="container" style="height: 400px"></div>

JavaScript

var chart = new Highcharts.Chart({
    chart: {
        renderTo: 'container',
        defaultSeriesType: 'column'
    },
    xAxis: {
        categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
    },
    plotOptions: {
        series: {
            allowPointSelect: false,
            events: {
                click: function (event) {
                    alert(event.point.customdata);
                }
            }
        }
    },
    series: [{
        customdata: {
            'somekey': 'Какие-то данные'
        },
        data : [{
            x: 5,
            y: 6,
        }]
    }]
});

alert(chart.series[0].options.customdata.somekey)