It’s baffling to me. Maybe I’m just used to using “modern” frameworks, but the only way this could be an issue is if you literally check if the string value equals “null” and then replace it with a null value.

lastName = lastName.ToUpper() == "NULL" ? null : lastName;

Either that or the database has some bug where it’s converting a string value of “null” into a null.

What makes them think they’re American? I don’t see any guns or medical bills piled up?