From 3c521d1cf2270b78b85831988fd0f530531978eb Mon Sep 17 00:00:00 2001
From: kom0055 <11908411+kom0055@users.noreply.github.com>
Date: Thu, 15 Oct 2026 01:24:02 +0800
Subject: [PATCH] Fix Equal nil dereference for null array elements

---
 equal_null_test.go    | 26 ++++++++++++++++++++++++++
 patch.go              |  4 ++++
 v5/equal_null_test.go | 26 ++++++++++++++++++++++++++
 v5/patch.go           |  4 ++++
 4 files changed, 60 insertions(+)
 create mode 100644 equal_null_test.go
 create mode 100644 v5/equal_null_test.go

diff --git a/equal_null_test.go b/equal_null_test.go
new file mode 100644
index 0000000..736bc51
--- /dev/null
+++ b/equal_null_test.go
@@ -0,0 +1,26 @@
+package jsonpatch
+
+import "testing"
+
+func TestEqualArraysContainingNull(t *testing.T) {
+	cases := []struct {
+		name, left, right string
+		want              bool
+	}{
+		{"null element", `[null]`, `[null]`, true},
+		{"null versus number", `[null]`, `[1]`, false},
+		{"number versus null", `[1]`, `[null]`, false},
+		{"null after value", `[true,null]`, `[true,null]`, true},
+		{"nested array", `[[null]]`, `[[null]]`, true},
+		{"object key order", `{"name":"test","data":[true,null]}`, `{"data":[true,null],"name":"test"}`, true},
+		{"different later value", `[null,1]`, `[null,2]`, false},
+	}
+	for i := range cases {
+		tc := cases[i]
+		t.Run(tc.name, func(t *testing.T) {
+			if got := Equal([]byte(tc.left), []byte(tc.right)); got != tc.want {
+				t.Fatalf("Equal(%s, %s) = %v, want %v", tc.left, tc.right, got, tc.want)
+			}
+		})
+	}
+}
diff --git a/patch.go b/patch.go
index 9513668..4d85322 100644
--- a/patch.go
+++ b/patch.go
@@ -180,6 +180,10 @@ func (n *lazyNode) tryAry() bool {
 }
 
 func (n *lazyNode) equal(o *lazyNode) bool {
+	if n == nil || o == nil {
+		return n == o
+	}
+
 	if n.which == eRaw {
 		if !n.tryDoc() && !n.tryAry() {
 			if o.which != eRaw {
diff --git a/v5/equal_null_test.go b/v5/equal_null_test.go
new file mode 100644
index 0000000..736bc51
--- /dev/null
+++ b/v5/equal_null_test.go
@@ -0,0 +1,26 @@
+package jsonpatch
+
+import "testing"
+
+func TestEqualArraysContainingNull(t *testing.T) {
+	cases := []struct {
+		name, left, right string
+		want              bool
+	}{
+		{"null element", `[null]`, `[null]`, true},
+		{"null versus number", `[null]`, `[1]`, false},
+		{"number versus null", `[1]`, `[null]`, false},
+		{"null after value", `[true,null]`, `[true,null]`, true},
+		{"nested array", `[[null]]`, `[[null]]`, true},
+		{"object key order", `{"name":"test","data":[true,null]}`, `{"data":[true,null],"name":"test"}`, true},
+		{"different later value", `[null,1]`, `[null,2]`, false},
+	}
+	for i := range cases {
+		tc := cases[i]
+		t.Run(tc.name, func(t *testing.T) {
+			if got := Equal([]byte(tc.left), []byte(tc.right)); got != tc.want {
+				t.Fatalf("Equal(%s, %s) = %v, want %v", tc.left, tc.right, got, tc.want)
+			}
+		})
+	}
+}
diff --git a/v5/patch.go b/v5/patch.go
index 83102e5..2e4216f 100644
--- a/v5/patch.go
+++ b/v5/patch.go
@@ -345,6 +345,10 @@ func (n *lazyNode) isNull() bool {
 }
 
 func (n *lazyNode) equal(o *lazyNode) bool {
+	if n == nil || o == nil {
+		return n == o
+	}
+
 	if n.which == eRaw {
 		if !n.tryDoc() && !n.tryAry() {
 			if o.which != eRaw {