required MM Boolean field w/ :default => false solution

validate_boolean_fields.rb

module ValidateBooleanFields
  extend ActiveSupport::Concern
  
  included do
    class_eval(<<-EOS, __FILE__, __LINE__)
      cattr_accessor :boolean_fields
    EOS
    
    validate :validate_boolean_fields
    
    def validate_boolean_fields
      self.class.class_variable_get(:@@boolean_fields).each do |boolean_field|
        errors[boolean_field] << "can't be blank" if self.send(boolean_field).nil?
      end
    end
  end
  
  module ClassMethods
    def validates_presence_of_boolean_fields(*fields)
      class_variable_set(:@@boolean_fields, fields)
    end
  end
end