Is that real undef values or just nulls/zeros formatted to be blank?
@aalex we did talk about this ages ago as a good feature for charts whether to plot zeros with a configurable true/false option. There would need to be some limited “smarts” around it e.g. subsitiute leading or trailing series of 0 with #NA in the Highcharts data frame (0s within the data series should still be plotted IMO just leading and trailing not).
In the meantime could @Ulas run a js function to basically do a find/replace for 0 to #NA in the grid before Highcharts renders?