Missing values in bar graph with wrong values showing wrong graph shape

Hi,
In stacked bar graph (and other types) when there is missing values it keeps the last known value, I would like to get a 0 value instead otherwise the bar graph global view is incorrect (showhing holes with a wrong value). I tried null values=null or =0 in “stackeing & Null value” but none work.
Something to do to get good graph shape ?
grafana 5.4.3

See black holes under bars.
barGraph
Regards