Hi Michael, your investigations were on the right track, and your example doc shows what exactly the problem is.
It’s nothing to do with
Concatenate itself, but just this bit:
thisRow.Email column is blank on the third row, that evaluates to
<undefined>.Email, and surely it breaks.
Now one option to fix it is to test if
thisRow.Email “exists”, returning
But probably the most concise way (in this specific case that the property you need is also the display column) is to use