code: func (b *EtcdBackend) Get(ctx context.Context, key []byte) (*backend.Item, error) {
  	re, err := b.client.Get(ctx, prependPrefix(key), clientv3.WithSerializable())
  	if err != nil {
  		return nil, convertErr(err)
  	}
  	if len(re.Kvs) == 0 {
  		return nil, trace.NotFound("item %q is not found", string(key))
  	}
  	kv := re.Kvs[0]
  	bytes, err := unmarshal(kv.Value)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  	return &backend.Item{Key: key, Value: bytes, ID: kv.ModRevision, LeaseID: kv.Lease}, nil
  }
docs: // Get returns a single item or not found error