Field is not Nullable Error (Calculate Field)

MatthewMcMillan1

Hi all, 

I am trying to populate a column 'Residentia' with YES or NO based on if another column (AllDetails) contains certain text.

When I run the below code, it gives me a 'Field is not nullable Error'

Can anyone advise?

Thanks!

DavidPike

if "rezone" in field:

    result = "YES"

else:

    result = "NO"

return result