From 8b7a43386445563e6e5f9be79849dc1f1ac6b463 Mon Sep 17 00:00:00 2001
From: Pavel Karpy <carpawell@nspcc.ru>
Date: Tue, 8 Jun 2021 15:30:27 +0300
Subject: [PATCH] [#302] pkg/container: Convert nil `Attribute` to nil message

Document that `Attribute.ToV2` method returns
`nil` when is called on `nil`. Add
corresponding unit test.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
---
 pkg/container/attribute.go      |  7 +++++++
 pkg/container/attribute_test.go | 15 +++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/pkg/container/attribute.go b/pkg/container/attribute.go
index 6f72c4c2..8964a048 100644
--- a/pkg/container/attribute.go
+++ b/pkg/container/attribute.go
@@ -29,10 +29,17 @@ func (a *Attribute) Value() string {
 	return (*container.Attribute)(a).GetValue()
 }
 
+// NewAttributeFromV2 wraps protocol dependent version of
+// Attribute message.
+//
+// Nil container.Attribute converts to nil.
 func NewAttributeFromV2(v *container.Attribute) *Attribute {
 	return (*Attribute)(v)
 }
 
+// ToV2 converts Attribute to v2 Attribute message.
+//
+// Nil Attribute converts to nil.
 func (a *Attribute) ToV2() *container.Attribute {
 	return (*container.Attribute)(a)
 }
diff --git a/pkg/container/attribute_test.go b/pkg/container/attribute_test.go
index a7a700d9..ea232867 100644
--- a/pkg/container/attribute_test.go
+++ b/pkg/container/attribute_test.go
@@ -4,10 +4,17 @@ import (
 	"testing"
 
 	"github.com/nspcc-dev/neofs-api-go/pkg/container"
+	containerv2 "github.com/nspcc-dev/neofs-api-go/v2/container"
 	"github.com/stretchr/testify/require"
 )
 
 func TestAttribute(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *container.Attribute
+
+		require.Nil(t, x.ToV2())
+	})
+
 	const (
 		key   = "key"
 		value = "value"
@@ -82,3 +89,11 @@ func TestAttributes(t *testing.T) {
 		}
 	})
 }
+
+func TestNewAttributeFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *containerv2.Attribute
+
+		require.Nil(t, container.NewAttributeFromV2(x))
+	})
+}