Rails - Turn empty strings into nil before validation

application_model.rb

class ApplicationModel < ActiveRecord::Base
  
  # http://stackoverflow.com/questions/1183506/make-blank-params-nil
  class_attribute :null_attrs
  self.null_attrs = %w(  )
  def nil_if_blank
    self.class.null_attrs.each { |attr|
      self[attr] = nil if self[attr].blank?
    }
  end
  
end

book.rb

class Book < ApplicationModel

  self.null_attrs = %w(title author)

end