Your data didn't really have empty values. It had empty rows in the sheet. In order to have disjoint line segments for the same series, you need to have at least one x-axis point with no value for the series. In the following image, you can see that there are gaps in the two series, but not in the Date column, which is used on the x-axis.

Here's a demo spreadsheet that showcases this gap method in order to create a Symbolic Dictionary.