Fix panic on private embedded interface

decode.go

@@ -549,9 +549,14 @@ func resetMap(out reflect.Value) {
 func (d *decoder) null(out reflect.Value) bool {
 	if out.CanAddr() {
 		switch out.Kind() {
-		case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
+		case reflect.Ptr, reflect.Map, reflect.Slice:
 			out.Set(reflect.Zero(out.Type()))
 			return true
+		case reflect.Interface:
+			if out.CanSet() {
+				out.Set(reflect.Zero(out.Type()))
+				return true
+			}
 		}
 	}
 	return false

decode_test.go

@@ -314,6 +314,16 @@ var unmarshalTests = []struct {
 		"a: YES",
 		&struct{ A bool }{true},
 	},
+	// Inlined interface
+	{
+		"a: 1\nb:\n  privateinterface: null\n",
+		&struct {
+			A int
+			B struct {
+				privateInterface
+			}
+		}{A: 1},
+	},
 
 	// Some cross type conversions
 	{

encode.go

@@ -110,7 +110,7 @@ func (e *encoder) marshalDoc(tag string, in reflect.Value) {
 
 func (e *encoder) marshal(tag string, in reflect.Value) {
 	tag = shortTag(tag)
-	if !in.IsValid() || in.Kind() == reflect.Ptr && in.IsNil() {
+	if !in.IsValid() || in.Kind() == reflect.Ptr && in.IsNil() || !in.CanInterface() {
 		e.nilv()
 		return
 	}

encode_test.go

@@ -30,6 +30,8 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
+type privateInterface interface{}
+
 var marshalIntTest = 123
 
 var marshalTests = []struct {
@@ -292,6 +294,17 @@ var marshalTests = []struct {
 		"a: 1\n",
 	},
 
+	// Inlined interface
+	{
+		&struct {
+			A int
+			B struct {
+				privateInterface
+			}
+		}{A: 1},
+		"a: 1\nb:\n    privateinterface: null\n",
+	},
+
 	// Struct inlining
 	{
 		&struct {