avoid html_safe? method call
use faster regex for String#blank?

Calculating -------------------------------------
              before      2687 i/100ms
               after      3867 i/100ms
-------------------------------------------------
              before    27978.4 (±2.0%) i/s -     142411 in   5.092192s
               after    40533.0 (±2.8%) i/s -     204951 in   5.060652s
short-circuit String#blank? if empty