as you can see in the example attacched If I Join (full outer join) 2 table on two keys (e.g. Native-Conuntry and Income) with 2 records cointaining missing (?, >50K) this 2 records are not associated, and are put on separate rows as if they were different. I think this is a bug.
Also because, if they were different, the Groupby Node should put them on different rows. But it does not happen so (as you can see the attached wokflow).
I worked with other softwares that don't have this problem. But anyway, how can I convert the null value into an empty string? I've tried with String Manipulation node (toEmpty($native-country$)) but then I have the same issue with the Join as you can see in the attached workflow.
You're almost there, Iiiaaa. :) You just have to set the String Replacer to Replace Column instead of Append Column. (Or join on the newly created column.) But it's even easier with the Missing Value node.