Just as in the post farther above, you need to write this into the cell for an empty string:
%""%
Or you can write this, as PAD will translate what you wrote above into this:
%''%
What you see in the screenshot in the flow is how PAD displays this line, i.e. minus the surrounding '%' s.
You can also see from my screenshots that the target cell does, in fact, display as empty.
