Rejecting a nested object if all attributes are blank

How do I reject the creation of an object if all of the attributes are
blank?

  accepts_nested_attributes_for :questions, :allow_destroy =>
true, :reject_if => lambda {|a| a.each.blank? }

You can do like this using all? method

accepts_nested_attributes_for :questions, :allow_destroy => true,
:reject_if => lambda { |attrs| attrs.all? { |k, v| v.blank?}}

Does that still reject the object if the id attribute is not blank?
Do I have to test each attribute separately and exclude the id
attribute in order for that to work?