Cannot save valid "Null" data

Possibly similar to CRM-2470, but using only the contact edit form (civicrm/contact/add&action=update)

Am unable to save valid data that consists of the string "Null", eg for a last name, nickname, etc

(Yup, we have a member with said last name)

It works if we prepend or append any printable nonwhitespace, but ugly;

Perhaps there is a way to special case this and not trim() a trailing whitespace to be stored in this instance?

(Ugly, but I imagine this might be a non-trivial problem. Am new - a pointer to the relevant file(s) would be appreciated)