Displaying Zero Values in a Chart

I have a spreadsheet that picks up monthly data from another spreadsheet and displays the data in a table and a chart. It obviously has formulas in for each month of the year and months April-Dec are returning the value of '0', since the data has yet to be input into the other spreadsheet for these months.
The problem is that my line graph looks like it plummets to 0 in April, whereas in fact I would just like the line to stop at March - how do I do this?
I have tried putting in an IF<0 formula, but "" still plots as 0!
The Charts tab on Options has the check box of 'plot empty cells as not plotted' checked and I have also tried hiding zero values in the spreadsheet, but neither of these work. Please help!

Try having your formula return an error instead of ""

Example:
=IF(A1>0,A1,NA())

Charts plot values, but not errors. Consequently, there will be no plummeting line.

Does that help?

Regards,
Ron