Graph column show also empty value

Hi all,

I have a graph with columns of radio button form field. I would like to show also the non-selected values in column graph, at the moment it shows only values that have been selected. For example my form question and radio button answers are:

How is it going?
- fine
- bad
- neutral

If no one has chosen neutral, the column (flat of course) "neutral" isn't shown in the graph. How can I show this zero value as a place holder also?

Thanks!