Replacing string with null in power query

Hey there

I'm trying to replace a text string in power query with power query's standard null value. However, whatever the text I try to replace with the null all I get is the same value all over (as show in the following image).

Why I do not simply replace it with ""? Because when I do so, I get two kind of blank values in my dataset:

I've came across with this post, but it does not fix my problem because I have to replace several values at once.

Do someone knows how to do that replacement?

Thanks in advance.