def valid?
      return false if @attribute_name.nil?
      return false if @attribute_name.to_s.length < 1
      sort_order_validator = EnumAttributeValidator.new('String', ["DESC", "ASC"])
      return false unless sort_order_validator.valid?(@sort_order)
      return true
    end
def valid?
      return false if @attribute_name.nil?
      return false if @attribute_name.to_s.length < 1
      sort_order_validator = EnumAttributeValidator.new('String', ["DESC", "ASC"])
      return false unless sort_order_validator.valid?(@sort_order)
      return true
    end
Check to see if the all the properties in the model are valid
 @return true if the model is valid