I found the reply myself in a question from another user similar to this issue.

I will use NA() instead of ""

Thank you that works!

"Data_Lisa" wrote:

When a chart is based on a formula e.g. =IF(A1=0;"";A1*B1) then the chart
will show the blank value "" as zero even if you whant to plot gaps or plot
the empty cell interpolated. Yes, I know Excel say empty cell and the cell is
not empty when there is a formula. Is there anybody who have found a "work
around"? I often have formulas that generate zero in the result but I want to
plot the result as if it was empty.