There are two possible solutions: Ensure the required size of the dataset, e.g. by creating it with the needed number of void entries and setting only the values computed. This leads to cell table contents like ? s.
Another solution is to back the original dataset by a fixed size string dataset holding the actual cell table entries. In the present case, the following FPScript fomula does the formatting and handles the non-existing data elements.

Dim sRes = "N/A" # 3	// "empty" cell

For Each Row i In sRes Do
	Try
		sRes = Format("%.0F s", MK)
	Catch ignore
	End
End

sRes

If named strMK one can change the cells content to
%%%
avoiding the error message since the genereted string dataset has the required length.