understand notions of cell emptiness

[jennybc]

When I use rexcel_read() on an xlsx that originated from a Google Sheet, empty cells show up in the linen object. Since the default Google Sheet has 1000 rows and 26 columns, for tiny test sheets, this constitutes the vast majority of the cells in the linen object.

@richfitz how well do you already understand cell emptiness? I bet native Excel sheets don't turn into linen objects with great gobs of empty cells, yes? If true, is that something you did explicitly or ...?