Null series values will break the line when rendering, missing values will be skipped
/* data stolen from http://howmanyleft.co.uk/vehicle/jaguar_'e'_type */
var day_data = [
{"period": "2012-10-01", "licensed": 3407},
{"period": "2012-09-30", "sorned": 0},
{"period": "2012-09-29", "sorned": 618},
{"period": "2012-09-20", "licensed": 3246, "sorned": 661},
{"period": "2012-09-19", "licensed": 3257, "sorned": null},
{"period": "2012-09-18", "licensed": 3248, "other": 1000},
{"period": "2012-09-17", "sorned": 0},
{"period": "2012-09-16", "sorned": 0},
{"period": "2012-09-15", "licensed": 3201, "sorned": 656},
{"period": "2012-09-10", "licensed": 3215}
];
Morris.Line({
element: 'graph',
data: day_data,
xkey: 'period',
ykeys: ['licensed', 'sorned', 'other'],
labels: ['Licensed', 'SORN', 'Other'],
/* custom label formatting with `xLabelFormat` */
xLabelFormat: function(d) { return (d.getMonth()+1)+'/'+d.getDate()+'/'+d.getFullYear(); },
/* setting `xLabels` is recommended when using xLabelFormat */
xLabels: 'day'
});