Plot empty point in line chart with previous non empty value

Hello,

I have a problem to plot series data in SSRS line chart, with the empty point, I don't want use average and zero provided by the report builder, I want use the last non empty data to fill the empty point, tried to use expression =Previous(Field!Value), no luck, any one have some good idea?

P.S. do not want to use query to fill the null with previous non null value, just from the performance point view. at last , the chart should have some line as square wave with different height, if I use average for empty point, it shows slop wave line which is not reflect the real production.

Thanks

Richard