code: def _delete_value(self, entity):
      
      if self._name in entity._values:
        del entity._values[self._name]
docs: Internal helper to delete the value for this Property from an entity.
  
      Note that if no value exists this is a no-op; deleted values will
      not be serialized but requesting their value will return None (or
      an empty list in the case of a repeated Property).