If anyone was strugling with formulas or any other function which require a null value to be displayed as zero, I found a solution (after a lot of hair pulling).
Use the Spreadsheet-Style Formula to concatenate a zero to the potentially null value. It will create a zero if the value is null else 04 if the value is (say) 4.
Formula: "A" & "B"
This concatenates the text value A and B into a single text value "AB"
Hope this helps 
