docs: def _get_convert_method(self):
          """
          Get right method to convert of the value.
          """
          for type_, method in self._map.items():
              if type(self.value) is bool and type_ is not bool:
                  continue
              if isinstance(self.value, type_):
                  return method
          if is_sql_instance(self.value):
              return self._raw
          return self._undefined