Replace if null

So, I’m working with tables and I’ve wanted to replace a cell’s text if it’s null.

In the screenshot should be the first row (on “cierre” column)

image.png2036×798 67 KB

I’ve tried using replace method but couldn’t work it out correctly.

I don’t know how to use the conditional method:

image.png1050×1302 108 KB

Isn’t any kind of conditional like: if something… then… for this values?