docs: def get_value(self, name, data):
          """
          Get the value of this field from the data.
          If there is a problem with the data, raise ValidationError.
  
          :param name: Name of this field (to retrieve from data).
          :param data: Dictionary of data for all fields.
          :raises: ValidationError
          :return: The value of this field.
          :rtype: any
          """
          if name in data:
              return data.get(name)
          if self.default:
              if callable(self.default):
                  return self.default()
              return self.default
          return None