def _prepare_for_put(self, entity):
    values = self._get_base_value_unwrapped_as_list(entity)
    for value in values:
      if value in None:
        value._prepare_for_put()
dataset/ETHPy150Open GoogleCloudPlatform/datastore-ndb-python/ndb/model.py/StructuredProperty._prepare_for_put/operator `is not` -> `in`