code: def _resolve_value(self, name):
          
          for instance in self.__instances():
              value = instance._resolve_value(name)
              if value:
                  return value
  
          # Otherwise, return an appropriate default value (populate_from)
          # TODO: This is duplicated in meta_models. Move this to a common home.
          if name in self.__metadata._meta.elements:
              populate_from = self.__metadata._meta.elements[name].populate_from
              if callable(populate_from):
                  return populate_from(None)
              elif isinstance(populate_from, Literal):
                  return populate_from.value
              elif populate_from is not NotSet:
                  return self._resolve_value(populate_from)
docs: Returns an appropriate value for the given name. 
              This simply asks each of the instances for a value.