code: func (ta KVProtoWriters) Put(key string, data proto.Message, opts ...PutOption) error {
  	var wasError error
  	for _, transport := range ta {
  		err := transport.Put(key, data, opts...)
  		if err != nil {
  			wasError = err
  		}
  	}
  	return wasError
  }
docs: // Put writes data to all aggregated transports.
  // This function implements KeyProtoValWriter.Put().