My recollection is clearly that it was on line  charts. I rarely do
column charts. However, it is entirely possible that I may have
simply Cleared the values  of the zero/blank cells. I also rarely do
plots of more than a few dozen values, so manual intervention for the
desired effect  is always a possiblity.

I am, however, still curious what the types of those cells  are...

So I checked. A Cleared cell  is Type "Empty".
A cell containing "" is an [obviously null] "String"...which, of
course, "makes sense"...

SO, perhaps a macro  to clear those pesky null cells (a copied
version) is in order.