def declared_attributes
      instance_values.select do |key, value|
        value != nil && self.class.xml_attributes.include?(key.to_sym)
      end
    end
def declared_attributes
      instance_values.select do |key, value|
        value != nil && self.class.xml_attributes.include?(key.to_sym)
      end
    end
A hash of instance variables that have been declared with
 seraialized_attributes and are not nil.
 This requires ruby 1.9.3 or higher