Problem with NORMSDIST function; how to deal with blanks?

So I'm using the NORMSDIST function to convert a bunch of z-scores to percentiles. The problem I'm having is that for some reason, it is treating blank data as 0; which totally messes up my percentiles, since a zero=50%. So, my question; how can I get around that? I was thinking maybe some sort of IF statement would work; you know, if the cell is empty, ignore it and then run the NORMSDIST function.

Any suggestions?

Thanks!

M.