[#302] pkg/reputation: Convert nil PeerID to nil message

Document that `PeerID.ToV2` method return `nil`
when called on `nil`. Document that `PeerIDFromV2`
function return `nil` when called on `nil`. Write
corresponding unit tests.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/reputation/peer.go

@@ -17,6 +17,8 @@ func NewPeerID() *PeerID {
 }
 
 // PeerIDFromV2 converts NeoFS API v2 reputation.PeerID message to PeerID.
+//
+// Nil reputation.PeerID converts to nil.
 func PeerIDFromV2(id *reputation.PeerID) *PeerID {
 	return (*PeerID)(id)
 }
@@ -28,6 +30,8 @@ func (x *PeerID) SetPublicKey(v [crypto.PublicKeyCompressedSize]byte) {
 }
 
 // ToV2 converts PeerID to NeoFS API v2 reputation.PeerID message.
+//
+// Nil PeerID converts to nil.
 func (x *PeerID) ToV2() *reputation.PeerID {
 	return (*reputation.PeerID)(x)
 }

pkg/reputation/peer_test.go

@@ -5,13 +5,22 @@ import (
 
 	"github.com/nspcc-dev/neofs-api-go/pkg/reputation"
 	reputationtest "github.com/nspcc-dev/neofs-api-go/pkg/reputation/test"
+	reputationV2 "github.com/nspcc-dev/neofs-api-go/v2/reputation"
 	"github.com/stretchr/testify/require"
 )
 
 func TestPeerID_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *reputation.PeerID
+
+		require.Nil(t, x.ToV2())
+	})
+
+	t.Run("nil", func(t *testing.T) {
 		peerID := reputationtest.GeneratePeerID()
 
 		require.Equal(t, peerID, reputation.PeerIDFromV2(peerID.ToV2()))
+	})
 }
 
 func TestPeerID_String(t *testing.T) {
@@ -50,3 +59,11 @@ func TestPeerIDEncoding(t *testing.T) {
 		require.Equal(t, id, id2)
 	})
 }
+
+func TestPeerIDFromV2(t *testing.T) {
+	t.Run("from nil", func(t *testing.T) {
+		var x *reputationV2.PeerID
+
+		require.Nil(t, reputation.PeerIDFromV2(x))
+	})
+}