Selecting Chart Point with None Value

After creating multiple datasets on a chart to achieve overlay the selection of a data point no longer works. In order for the category axis to match up I had to place None rows for the datasets to have equal lengths. Now when I click on a point it will not show as being selected and the selectedData property returns the last row in the data set with None no matter where I click on the graph. Is there any way to control which datasets can be selected and which ones cannot?