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Advocate I
Advocate I

Expected String but got Null fix on lookup field using fx expressions


I have encountered this issue where im trying to duplicate invoice (screen1) but system wants all fields filled even the non mandatory ones if not it comes with an error expected string but got null and flow wont even run. I have searched for many possibilites of fixing this by fx expressions (screen2) and came with and condition that should work. Unfortunatley the error is still there and I dont know why. In my case Im trying to fill the field opportunities with empty string to avoid null beacuse the field is not mandatory and sometimes it will be filled sometimes not. In the end with the current fx expression flow will run but wont transfer for example the lookup field even if its filled.





Super User
Super User

Hi @OndrejBriza 


Your expression in the concat, will be evaluated as a string (the full expression will be a string) and not the value of the expression.  Try removing the concat.  To test, put that expression in a compose to see it being evaluated via the flow history.



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