It is completely nit-picky, as others have said, both methods have pluses/minuses, so how does the interviewer know the internal preference of the hiring compan

It is completely nit-picky, as others have said, both methods have pluses/minuses, so how does the interviewer know the internal preference of the hiring company? Unless the question was specifically "how would you do this lookup if you have Dirty data". Then maybe missing using a default value is something. But even then, maybe you hit an invalid value, you should fail, or if you are providing defaults then there should be some follow up on, what is a good default, how will defaults be reported out, etc....