fix: skip encoding an inline field if it is null

encode.go

@@ -823,6 +823,10 @@ func (e *Encoder) encodeStruct(ctx context.Context, value reflect.Value, column
 			}
 			mapNode, ok := value.(ast.MapNode)
 			if !ok {
+				// if an inline field is null, skip encoding it
+				if _, ok := value.(*ast.NullNode); ok {
+					continue
+				}
 				return nil, xerrors.Errorf("inline value is must be map or struct type")
 			}
 			mapIter := mapNode.MapRange()

encode_test.go

@@ -16,8 +16,10 @@ import (
 	"github.com/goccy/go-yaml/ast"
 )
 
-var zero = 0
-var emptyStr = ""
+var (
+	zero     = 0
+	emptyStr = ""
+)
 
 func TestEncoder(t *testing.T) {
 	tests := []struct {
@@ -643,12 +645,12 @@ func TestEncoder(t *testing.T) {
 		// time value
 		{
 			"v: 0001-01-01T00:00:00Z\n",
-			map[string]time.Time{"v": time.Time{}},
+			map[string]time.Time{"v": {}},
 			nil,
 		},
 		{
 			"v: 0001-01-01T00:00:00Z\n",
-			map[string]*time.Time{"v": &time.Time{}},
+			map[string]*time.Time{"v": {}},
 			nil,
 		},
 		{
@@ -980,6 +982,30 @@ c: true
 	}
 }
 
+func TestEncoder_InlineNil(t *testing.T) {
+	type base struct {
+		A int
+		B string
+	}
+	var buf bytes.Buffer
+	enc := yaml.NewEncoder(&buf)
+	if err := enc.Encode(struct {
+		*base `yaml:",inline"`
+		C     bool
+	}{
+		C: true,
+	}); err != nil {
+		t.Fatalf("%+v", err)
+	}
+	expect := `
+c: true
+`
+	actual := "\n" + buf.String()
+	if expect != actual {
+		t.Fatalf("inline marshal error: expect=[%s] actual=[%s]", expect, actual)
+	}
+}
+
 func TestEncoder_Flow(t *testing.T) {
 	var buf bytes.Buffer
 	enc := yaml.NewEncoder(&buf, yaml.Flow(true))
@@ -1014,7 +1040,7 @@ func TestEncoder_FlowRecursive(t *testing.T) {
 		M map[string][]int `yaml:",flow"`
 	}
 	v.M = map[string][]int{
-		"test": []int{1, 2, 3},
+		"test": {1, 2, 3},
 	}
 	var buf bytes.Buffer
 	if err := yaml.NewEncoder(&buf).Encode(v); err != nil {
@@ -1311,6 +1337,7 @@ func (t *tMarshal) MarshalYAML() ([]byte, error) {
 	}
 	return buf.Bytes(), nil
 }
+
 func Test_Marshaler(t *testing.T) {
 	const expected = `- hello-world
 `
@@ -1365,10 +1392,12 @@ type FastMarshaler struct {
 	A string
 	B int
 }
-type TextMarshaler int64
-type TextMarshalerContainer struct {
-	Field TextMarshaler `yaml:"field"`
-}
+type (
+	TextMarshaler          int64
+	TextMarshalerContainer struct {
+		Field TextMarshaler `yaml:"field"`
+	}
+)
 
 func (v SlowMarshaler) MarshalYAML() ([]byte, error) {
 	var buf bytes.Buffer