Setting `userAbout` field to `Nothing` if empty

Some HN users (e.g. zinfandel) simply doesn't have `about` field that
case results to `Nothing` in User's record. Others (e.g. root) have it but it's
empty. It seems that it's a good idea to turn such empty fields into `Nothing`.
Merge pull request #1 from zudov/empty_about_field

Setting `userAbout` field to `Nothing` if empty