Highcharts.chart('container', {

    chart: {
        type: 'area'
    },
    title: {
        text: 'stacking: normal, connectNulls: true'
    },
    plotOptions: {
        area: {
            connectNulls: true,
            stacking: 'normal'
        }
    },
    series: [{
        type: 'area',
        data: [1, 1, null, 1, 1, 1]
    }, {
        type: 'area',
        data: [1, 1, 1, null, 1, 1]
    }]

});