Fix Equal panic for null array elements

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)
+			}
+		})
+	}
+}

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 {

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)
+			}
+		})
+	}
+}

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 {