From c8e4270e391da31c25848aa10e3fdb60c554fe35 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Frank=20Schr=C3=B6der?= <frank.schroeder@northvolt.com>
Date: Mon, 22 Nov 2021 11:50:04 +0100
Subject: [PATCH 1/2] ua: encode nil NodeIDs as two byte zero ids

This patch encodes a 'nil' NodeID as a two byte zero node id.

See #506
---
 ua/node_id.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/ua/node_id.go b/ua/node_id.go
index 721845cf..6585ece4 100644
--- a/ua/node_id.go
+++ b/ua/node_id.go
@@ -405,6 +405,12 @@ func (n *NodeID) Decode(b []byte) (int, error) {
 }
 
 func (n *NodeID) Encode() ([]byte, error) {
+	// https://github.com/gopcua/opcua/issues/506
+	// encode 'nil' node ids as two byte zero values
+	if n == nil {
+		return []byte{0, 0}, nil
+	}
+
 	buf := NewBuffer(nil)
 	buf.WriteByte(byte(n.mask))
 

From 19eef56c860a43a9121c94e32d9b59afba44be7c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Frank=20Schr=C3=B6der?= <frank.schroeder@northvolt.com>
Date: Mon, 22 Nov 2021 12:01:04 +0100
Subject: [PATCH 2/2] ua: test encode nil node id as zero

---
 ua/node_id_test.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/ua/node_id_test.go b/ua/node_id_test.go
index 72bc5fa4..9e4e89bc 100644
--- a/ua/node_id_test.go
+++ b/ua/node_id_test.go
@@ -12,6 +12,7 @@ import (
 	"testing"
 
 	"github.com/gopcua/opcua/errors"
+	"github.com/pascaldekloe/goe/verify"
 )
 
 func TestNodeID(t *testing.T) {
@@ -132,6 +133,15 @@ func BenchmarkReflectDecode(b *testing.B) {
 	}
 }
 
+func TestEncodeNilNodeID(t *testing.T) {
+	var n *NodeID
+	b, err := n.Encode()
+	if err != nil {
+		t.Fatalf("got error %v want %v", err, nil)
+	}
+	verify.Values(t, "", b, []byte{0, 0})
+}
+
 func TestParseNodeID(t *testing.T) {
 	cases := []struct {
 		s   string