Text labels can be used to display the value next to each data point.
Edit the Series Settings, in tab Advanced, check Value Labels :
With the following result for example :
By default, when the Y Value is NULL, the chart doesn’t display any shape.
Instead, you can force to display a point with a predefined value for NULL values.
Edit the Series Settings, in tab Advanced, check Plot Null Values :
For example, in the following chart, there are NULL values after a certain date (data unknown) :
Instead of a broken line, you may choose to display those unknown values as 0 with a red point :