rails 文字列に対するpresent?

nil?
empty?
はrubyのメソッドですが、

present?
blank?
はrailsのメソッドです。

文字列に対しては以下のようになります。

$ rails console
Loading development environment (Rails 4.2.2)
irb(main):001:0> a = nil
=> nil
irb(main):002:0> b = " "
=> " "
irb(main):003:0> c = "  "
=> "  "
irb(main):004:0> d = "h"
=> "h"
irb(main):005:0> a.present?
=> false
irb(main):006:0> b.present?
=> false
irb(main):007:0> c.present?
=> false
irb(main):008:0> d.present?
=> true