Detecting Sum formula "null" value
I have a simple sheet with a mixture of parent and child rows. Not all parent rows have child rows. I have a very simple formula [=SUM(CHILDREN())] to sum the value of child rows for a parent row where they exist. Where there are no child rows the formula returns a "0". I use conditional formatting to change the colour of a cell based on the value from the SUM formula. This works fine for any value returned other than the null value where there are no child rows. I want to change the text colour to the background of these "null" value cells so they appear blank rather than showing "0", but can't work out what the "0" returned actually is. I have tried all the variations in the conditional formatting options with no luck. Any one know what "value" is returned by my formula when there are no child rows?