[#302] pkg/object: Document default values set in `NewAddress`

Document field values of instance constructed via `NewAddress`.
Assert the values in corresponding unit test.

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

pkg/object/address.go

@@ -28,6 +28,10 @@ func NewAddressFromV2(aV2 *refs.Address) *Address {
 // NewAddress creates and initializes blank Address.
 //
 // Works similar as NewAddressFromV2(new(Address)).
+//
+// Defaults:
+// 	- cid: nil;
+//	- oid: nil.
 func NewAddress() *Address {
 	return NewAddressFromV2(new(refs.Address))
 }

pkg/object/address_test.go

@@ -101,3 +101,19 @@ func TestAddress_ToV2(t *testing.T) {
 		require.Nil(t, x.ToV2())
 	})
 }
+
+func TestNewAddress(t *testing.T) {
+	t.Run("default values", func(t *testing.T) {
+		a := NewAddress()
+
+		// check initial values
+		require.Nil(t, a.ContainerID())
+		require.Nil(t, a.ObjectID())
+
+		// convert to v2 message
+		aV2 := a.ToV2()
+
+		require.Nil(t, aV2.GetContainerID())
+		require.Nil(t, aV2.GetObjectID())
+	})
+}