code: def validate(self, request, value):
          
          if self.required and value == DEFAULT_FIELD_VALUE:
              return ValidationResult(is_success=False,
                                      reason='This field is required')
          if not self.nullable and value is None:
              return ValidationResult(is_success=False,
                                      reason='null is not a valid value')
          return ValidationResult(is_success=True)
docs: This is not for business validation
          This should be only used for type validation
          Hence the only input is the value of the field
          :param value:
          :return: