Distinguish between blank and zero in org-mode spreadsheet

[Bob Newell <bobnewell@bobnewell.net>]

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Can't find out about this anywhere.  My apologies if I missed something
simple or something already posted.

I want a calculation to appear in column 9 if and only if column 2 is
non-blank. If there is an explicit 0 in column 2, I want the calculation to
appear in column 9. But if column 2 is blank, I also want column 9 to be
blank.

I made it work with the following elisp example:

$9 = '(if (eq $2 "") "" (* (string-to-number @2$8) (string-to-number $1)));S

But the question is, can it be made to work with a calc formula, which
would be possibly a little more straightforward? All of the other columns
have the same requirement, and some of the formulas are quite long, so
doing many, many string-to-number functions makes things very cluttered.

The problem obviously revolves around a blank cell being interpreted as
zero. That's all well and good, and quite correct, but makes distinguishing
blank and explicit zero more difficult.

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