On Feb 19, 10:39 am, I wrote:
Well, I am assured that you can leave the formula as you had it and
simply set up a custom formula. But I have not yet figured the
correct syntax :-(.

The Help documentation for custom formats leaves a lot to be desired.
But the following might suffice, if you currently use the General
format:

general;-general;

However, if you null values for zeros for the entire spreadsheet, you
could uncheck Tools - Options - View - Zero Values.

But I usually avoid "format" options that affect the entire
spreadsheet.