code: def _firestore_api(self):
          
          if self._firestore_api_internal is None:
              self._firestore_api_internal = firestore_client.FirestoreClient(
                  credentials=self._credentials
              )
  
          return self._firestore_api_internal
docs: Lazy-loading getter GAPIC Firestore API.
  
          Returns:
              ~.gapic.firestore.v1beta1.firestore_client.FirestoreClient: The
              GAPIC client with the credentials of the current client.