copying empty cells, or not

[John Denker <jsd av8n com>]

Hi --

There are many situations where it is desirable to copy data from
one region to another on the spreadsheet.  This is particularly
common when part of one sheet tracks part of another sheet.

AFAICT, copying is nontrivial when the source contains empty cells.

The simple "=" operator converts an empty cell into an explicit
numerical zero, which is very often not what is desired.  In
particular, a great many functions including len(), count(),
average() etc. treat zero very differently from empty.

On possibility is to explicitly check if the source is empty, and
if so to set the destination to the null string.
        =if(a1<>"",a1,"")
This works for most purposes, although not for the type() function
and not for comparison to zero using (...=0) or (...<>0).

Question: Is there any way for a calculation to assign the "empty"
status to a cell?

Question: If not, is there a standard workaround?  My practice
has been to use the null string as a substitute for empty, and
to never rely on the type() function or the zero-comparison
operators without defensively checking the count() beforehand.

Is there a better workaround?  Is there a better way to think
about these concepts?  Is this documented somewhere?  In particular,
is there an authoritative list of which functions and operators
we have to be defensive about?