Remove Space on Bar Charts for Missing Data

I am trying to create a bar chart that shows student achievement results
across a number of years. For some of the schools, I do not have data in
certain years. I do not want the chart to leave a big space for this missing
data - I just want it to display the data that I have without leaving this
huge gap for the empty cells in the table it is linked to. I tried putting
=NA() in the empty cells but the chart is still leaving gaps. Is there any
way to have the chart wizard ignore the empty spaces so that it will just
display the data that I have?
Thanks!