code: func ValidateValuer(field reflect.Value) interface{} {
  
  	if valuer, ok := field.Interface().(driver.Valuer); ok {
  
  		val, err := valuer.Value()
  		if err == nil {
  			return val
  		}
  		// handle the error how you want
  	}
  
  	return nil
  }
docs: // ValidateValuer implements validator.CustomTypeFunc