Mike generally you're going to need to do a wee bit more explaining, but that said try something like this:
ZN([Number of Records])
This function converts NULL values to zeros. But a lot depends on whether your field contains NULL values or blanks. There's a lot written on this distinction and how Tableau pads things, and under what circumstances. So if this doesn't work for you, post a package workbook (twbx) so the folks who understand padding (I don't) can give you a hand.