code: func FilterShutdownErrors(err error) error {
  	if err == nil {
  		return nil
  	}
  	if strings.Contains(err.Error(), "use of closed network connection") {
  		return nil
  	}
  	return err
  }
docs: // FilterShutdownErrors returns the input error, with the exception of "use of
  // closed network connection," on which it returns nil
  // Per https://github.com/grpc/grpc-go/issues/1017, a gRPC server's `Serve()`
  // will always return an error, even when GracefulStop() is called. We don't
  // want to log graceful stops as errors, so we filter out the meaningless
  // error we get in that situation.