なぜか boolean の validates ~ presence がいつもエラーになる ref: http://qiita.com/diskshima/items/9c0b6286d68c0c13bb68

file0.rb

class Person < ActiveRecord::Base
  validates :name, presence: true
end

file1.txt

class Person < ActiveRecord::Base
  validates :name, presence: true
  validates :has_glasses, presence: true
end

file2.rb

irb> person = Person.new(name: "Daisuke", has_glasses: false)
 => #<Person id: nil, name: "Daisuke", has_glasses: false>
irb> person.has_glasses
 => false
irb> person.valid?
=> false

file3.rb

class PresenceValidator < EachValidator
  def validate_each(record, attr_name, value)
    record.errors.add(attr_name, :blank, options) if value.blank?
  end
end

file4.rb

irb> value = false
=> false
irb> value.blank?
 => true

file5.rb

def blank?
  respond_to?(:empty?) ? !!empty? : !self
end

file6.rb

validates :has_glasses, inclusion: [true, false]