How to return a blank in formula column looking up at a column connected to another board

Hi everyone. I am new to I am attempting to set up a booking system using a pool of freelance workers. However, I need a column to generate a reference for each booking. Due to GDPR, I need to initialise the name of customers (residing in a connected board).

To do this I used this formula:

if(len({Customers#Names})-len(SUBSTITUTE({Customers#Names}," “,”“))=0,left({Customers#Names},1),if(len({Customers#Names})-len(SUBSTITUTE({Customers#Names},” “,”“))=1,left({Customers#Names},1)&mid({Customers#Names},find(” “,{Customers#Names})+1,1),left({Customers#Names},1)&mid({Customers#Names},find(” “,{Customers#Names})+1,1)&mid({Customers#Names},find(” “,{Customers#Names},find(” ",{Customers#Names})+1)+1,1)))

This return the initials of the customers where 1st name and surname is providing.

However, whenever there is no customer has been selected but the booking has been setup, the formula column returns a red exclamation mark saying “one of the parameters is invalid”. So I tried to insert a IF…ISBLANK () condition in the formula, it doesn’t work.

I am thinking maybe IsBlank() is not the right function to look up a connected board column to determine if it is blank or not. Can anyone advise?