Dynamic text on decomposition tree tooltip

Hi Community!

I am using Decomposition tree as one of my visuals, and as a complete newbie I came across an issue with one of my tooltips. 

In my model there is Customer table, and it has a calcutaded column [Customer Name]. [Customer Name] is a concatenation of two other columns in that same table, in case of incorrect values it just stores 'N/A' - this logic must stay for some other work on the model, which is not mine.

Now, I have tooltip page designed for that tree which contains a card, as of now it displays the [Customer Name] value. What I can't figure out is how do I create a function that would allow to display [Customer Name] only when value is different that 'N/A'.

I know it can be solved by a simple IF, but when I try to write it in Tabular I cannot reference [Customer Name] by any means... Could you help me understand why?