I have given value to 1st and last column. Here is an example.
const data = new google.visualization.DataTable();
data.addColumn('date', 'Day');
data.addColumn('number', 'label 1');
data.addColumn('number', 'label 2');
data.addColumn('number', 'label 3');
data.addRows([
[new Date("2016-8-1"),40, 10, 2],
[new Date("2016-8-2"),null,null,null],
[new Date("2016-8-3"),null,null,null],
[new Date("2016-8-4"),null,null,null],
[new Date("2016-8-5"),null,null,null],
[new Date("2016-8-6"),20,30,20]
]);
Here is the result i am getting.
The Chart works when we have any value in the middle rather than null.