From 941b513eb3d8b247c5a31cf96b60a71349b5904a Mon Sep 17 00:00:00 2001
From: Pavel Karpy <carpawell@nspcc.ru>
Date: Tue, 8 Jun 2021 18:50:45 +0300
Subject: [PATCH] [#302] pkg/object: Convert nil `Attribute` to nil message

Document that `Attribute.ToV2` method return `nil`
when called on `nil`. Document that `NewAttributeFromV2`
function return `nil` when called on `nil`. Write
corresponding unit tests.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
---
 pkg/object/attribute.go      |  4 ++++
 pkg/object/attribute_test.go | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/pkg/object/attribute.go b/pkg/object/attribute.go
index cbc318dc..23be55d2 100644
--- a/pkg/object/attribute.go
+++ b/pkg/object/attribute.go
@@ -8,6 +8,8 @@ import (
 type Attribute object.Attribute
 
 // NewAttributeFromV2 wraps v2 Attribute message to Attribute.
+//
+// Nil object.Attribute converts to nil.
 func NewAttributeFromV2(aV2 *object.Attribute) *Attribute {
 	return (*Attribute)(aV2)
 }
@@ -40,6 +42,8 @@ func (a *Attribute) SetValue(v string) {
 }
 
 // ToV2 converts Attribute to v2 Attribute message.
+//
+// Nil Attribute converts to nil.
 func (a *Attribute) ToV2() *object.Attribute {
 	return (*object.Attribute)(a)
 }
diff --git a/pkg/object/attribute_test.go b/pkg/object/attribute_test.go
index a4ab8ae5..05735b75 100644
--- a/pkg/object/attribute_test.go
+++ b/pkg/object/attribute_test.go
@@ -3,6 +3,7 @@ package object
 import (
 	"testing"
 
+	"github.com/nspcc-dev/neofs-api-go/v2/object"
 	"github.com/stretchr/testify/require"
 )
 
@@ -47,3 +48,19 @@ func TestAttributeEncoding(t *testing.T) {
 		require.Equal(t, a, a2)
 	})
 }
+
+func TestNewAttributeFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *object.Attribute
+
+		require.Nil(t, NewAttributeFromV2(x))
+	})
+}
+
+func TestAttribute_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *Attribute
+
+		require.Nil(t, x.ToV2())
+	})
+}