code: def _get_value(self, entity):
      
      if entity._projection:
        if self._name not in entity._projection:
          raise UnprojectedPropertyError(
              'Property %s is not in the projection' % (self._name,))
      return self._get_user_value(entity)
docs: Internal helper to get the value for this Property from an entity.
  
      For a repeated Property this initializes the value to an empty
      list if it is not set.