code: def _get_value(self, entity):
      
      value = self._get_user_value(entity)
      if value is None and entity._projection:
        # Invoke super _get_value() to raise the proper exception.
        return super(StructuredProperty, self)._get_value(entity)
      return value
docs: Override _get_value() to *not* raise UnprojectedPropertyError.