docs: private Key insert(Entity entity) throws DatastoreException {
      CommitRequest req = CommitRequest.newBuilder()
  	.addMutations(Mutation.newBuilder()
  	    .setInsert(entity))
          .setMode(CommitRequest.Mode.NON_TRANSACTIONAL)
  	.build();
      return datastore.commit(req).getMutationResults(0).getKey();
    }