Frank Kabel wrote...
=IF(A2<"","",B1)

Reread the OP's second paragraph.

OP wrote:
I am trying to effect a null cell value based on a formula. For
example, for B2, I might want to have B2 be NULL if A2 is NOT NULL,
otherwise use the value from B1). This might be written something
like "=if(A2"",NULL,B1)".

For the OP: your terminology is incorrect. 'Null' cells are those containing
the error value #NULL!. If you mean cells containing nothing, the correct
term is 'blank'.

The intent is to allow the text value of A2 to extend into B2 (i.e.
not wrap). Entering a "" for the TRUE action does not allow A2 to
extend into B2.

If cell B2 contains anything whatsoever, it can't be blank ('blank' being
defined as the complete absence of any contents), and text in cell A2 can't
extend into cell B2. You just can't do this in Excel or any other
spreadsheet of which I'm aware (and unlike most of the other participants in
this ng, I use a half dozen others over the course of an average week).

If you want A2 to extend into B2, then B2 simply can't contain anything at
all. Period. Time to redesign or adapt.