Over in a cumulative total provides blank values

I have built a bar chart visualization with Spotfire that includes the use of the Over function to give a running total. Months are on the X axis and counts are on the Y axis. My data set contains months where there were no values. When I graph that there is no bar for months not containing a value although a running total should still contain a value, since previous total plus zero should still be the previous total.

How do I get a month with no value to still show a bar for that month?

Custom Expression for the Y axis is this:

Count() OVER (AllPrevious(Axis.X))

(1) Answer