Affirmative conditionals

I believe these "affirmative" conditionals express the intention of the code much better than their "negative" counterparts.

Moreover, In this case we don't return `true` if either field is `blank`.

Only gotcha is that `persisted?` also checks if a record is `!destroyed?`, which `new_record?` obviously doesn't.
In this case though, I believe, that check is superfluous.