code: def instance_admin_client(self):
          
          if self._instance_admin_client is None:
              if not self._admin:
                  raise ValueError("Client is not an admin client.")
              self._instance_admin_client = _create_gapic_client(
                  bigtable_admin_v2.BigtableInstanceAdminClient
              )(self)
          return self._instance_admin_client
docs: Getter for the gRPC stub used for the Table Admin API.
  
          For example:
  
          .. literalinclude:: snippets.py
              :start-after: [START bigtable_instance_admin_client]
              :end-before: [END bigtable_instance_admin_client]
  
          :rtype: :class:`.bigtable_admin_pb2.BigtableInstanceAdmin`
          :returns: A BigtableInstanceAdmin instance.
          :raises: :class:`ValueError <exceptions.ValueError>` if the current
                   client is not an admin client or if it has not been
                   :meth:`start`-ed.