nil?

# File activerecord/lib/active_record/relation/query_attribute.rb, line 37
      def nil?
        unless value_before_type_cast.is_a?(StatementCache::Substitute)
          value_before_type_cast.nil? ||
            (type.respond_to?(:subtype) || type.respond_to?(:normalizer)) && serializable? && value_for_database.nil?
        end
      end