Revert "Merge pull request #9784 from vipulnsward/change_from_blank_to_empty_on_string"

This reverts commit 9c4c05fc82e997b722dec4068c3aa27eaee69eb8, reversing
changes made to 4620bdcefd0c88905a005f191496df887877b8f3.

Reason: They're not completely interchangeable, since blank? will also
check for strings containing spaces.