[#302] pkg/netmap: Convert nil `NetworkInfo` to nil message

Document that `NetworkInfo.ToV2` method return `nil`
when called on `nil`. Document that `NewNetworkInfoFromV2`
function return `nil` when called on `nil`. Write
corresponding unit tests.

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

pkg/netmap/network_info.go

@@ -9,6 +9,8 @@ import (
 type NetworkInfo netmap.NetworkInfo
 
 // NewNetworkInfoFromV2 wraps v2 NetworkInfo message to NetworkInfo.
+//
+// Nil netmap.NetworkInfo converts to nil.
 func NewNetworkInfoFromV2(iV2 *netmap.NetworkInfo) *NetworkInfo {
 	return (*NetworkInfo)(iV2)
 }
@@ -19,6 +21,8 @@ func NewNetworkInfo() *NetworkInfo {
 }
 
 // ToV2 converts NetworkInfo to v2 NetworkInfo.
+//
+// Nil NetworkInfo converts to nil.
 func (i *NetworkInfo) ToV2() *netmap.NetworkInfo {
 	return (*netmap.NetworkInfo)(i)
 }

pkg/netmap/network_info_test.go

@@ -51,3 +51,17 @@ func TestNetworkInfoEncoding(t *testing.T) {
 		require.Equal(t, i, i2)
 	})
 }
+
+func TestNewNetworkInfoFromV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		require.Nil(t, NewNetworkInfoFromV2(nil))
+	})
+}
+
+func TestNetworkInfo_ToV2(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		var x *NetworkInfo
+
+		require.Nil(t, x.ToV2())
+	})
+}