def valid?
      sort_field_validator = EnumAttributeValidator.new('String', ["DEFAULT", "CREATED_AT"])
      return false unless sort_field_validator.valid?(@sort_field)
      sort_order_validator = EnumAttributeValidator.new('String', ["DESC", "ASC"])
      return false unless sort_order_validator.valid?(@sort_order)
      return true
    end
def valid?
      sort_field_validator = EnumAttributeValidator.new('String', ["DEFAULT", "CREATED_AT"])
      return false unless sort_field_validator.valid?(@sort_field)
      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