kovidgoyal/calibre — pull request #291 by cbhaley (2014-08-24 16:16:26+00:00)
Title: Fix #1360806: allow book.smart_update to copy "null" (Unknown) author ...

...information to the destination if the destination author and author_sort values are null. There is a small performance hit if the source of the copy is null, which fortunately is rather rare. This change better supports non-null author_sort values associated with null author values.