raise exception on attempted mass assignment of a protected attribute

mass_assignment_exception.rb

# monkey-patch to raise an exception when attempting to mass-assign a protected attr
# more info: http://is.gd/MiA1mn
module ActiveModel
  module MassAssignmentSecurity
    module Sanitizer
    protected
      def warn!(attrs)
        self.logger.debug "WARNING: Can't mass-assign protected attributes: #{attrs.join(', ')}" if self.logger
        raise RuntimeError, "these attributes are protected from mass assignment, use `attr_accessible :#{attrs.join(', :')}`"
      end
    end
  end
end

it'd be great to also add in the name of failing class. wasn't immediately obvious to me so I left it. suggestions welcomed. :-)