Supports decoding for null value

decode.go

@@ -228,6 +228,11 @@ func (d *Decoder) decodeValue(dst reflect.Value, src ast.Node) error {
 		if dst.IsNil() {
 			return nil
 		}
+		if src.Type() == ast.NullType {
+			// set nil value to pointer
+			dst.Set(reflect.Zero(valueType))
+			return nil
+		}
 		v := d.createDecodableValue(dst.Type())
 		if err := d.decodeValue(v, src); err != nil {
 			return errors.Wrapf(err, "failed to decode ptr value")
@@ -399,6 +404,11 @@ func (d *Decoder) decodeStruct(dst reflect.Value, src ast.Node) error {
 			if !fieldValue.CanSet() {
 				return xerrors.Errorf("cannot set embedded type as unexported field %s.%s", field.PkgPath, field.Name)
 			}
+			if fieldValue.Type().Kind() == reflect.Ptr && src.Type() == ast.NullType {
+				// set nil value to pointer
+				fieldValue.Set(reflect.Zero(fieldValue.Type()))
+				continue
+			}
 			newFieldValue := d.createDecodableValue(fieldValue.Type())
 			if err := d.decodeValue(newFieldValue, src); err != nil {
 				if xerrors.Is(err, errOverflowNumber) {
@@ -416,6 +426,11 @@ func (d *Decoder) decodeStruct(dst reflect.Value, src ast.Node) error {
 			continue
 		}
 		fieldValue := structValue.Elem().FieldByName(field.Name)
+		if fieldValue.Type().Kind() == reflect.Ptr && src.Type() == ast.NullType {
+			// set nil value to pointer
+			fieldValue.Set(reflect.Zero(fieldValue.Type()))
+			continue
+		}
 		newFieldValue := d.createDecodableValue(fieldValue.Type())
 		if err := d.decodeValue(newFieldValue, v); err != nil {
 			if xerrors.Is(err, errOverflowNumber) {
@@ -461,6 +476,11 @@ func (d *Decoder) decodeSlice(dst reflect.Value, src ast.Node) error {
 	elemType := sliceType.Elem()
 	for iter.Next() {
 		v := iter.Value()
+		if elemType.Kind() == reflect.Ptr && v.Type() == ast.NullType {
+			// set nil value to pointer
+			sliceValue = reflect.Append(sliceValue, reflect.Zero(elemType))
+			continue
+		}
 		dstValue := d.createDecodableValue(elemType)
 		if err := d.decodeValue(dstValue, v); err != nil {
 			return errors.Wrapf(err, "failed to decode value")
@@ -484,6 +504,15 @@ func (d *Decoder) decodeMap(dst reflect.Value, src ast.Node) error {
 	for mapIter.Next() {
 		key := mapIter.Key()
 		value := mapIter.Value()
+		k := reflect.ValueOf(d.nodeToValue(key))
+		if k.IsValid() && k.Type().ConvertibleTo(keyType) {
+			k = k.Convert(keyType)
+		}
+		if valueType.Kind() == reflect.Ptr && value.Type() == ast.NullType {
+			// set nil value to pointer
+			mapValue.SetMapIndex(k, reflect.Zero(valueType))
+			continue
+		}
 		dstValue := d.createDecodableValue(valueType)
 		if err := d.decodeValue(dstValue, value); err != nil {
 			if xerrors.Is(err, errOverflowNumber) {
@@ -492,8 +521,12 @@ func (d *Decoder) decodeMap(dst reflect.Value, src ast.Node) error {
 			}
 			return errors.Wrapf(err, "failed to decode value")
 		}
-		castedKey := reflect.ValueOf(d.nodeToValue(key)).Convert(keyType)
-		mapValue.SetMapIndex(castedKey, d.castToAssignableValue(dstValue, valueType))
+		if !k.IsValid() {
+			// expect nil key
+			mapValue.SetMapIndex(d.createDecodableValue(keyType), d.castToAssignableValue(dstValue, valueType))
+			continue
+		}
+		mapValue.SetMapIndex(k, d.castToAssignableValue(dstValue, valueType))
 	}
 	dst.Set(mapValue)
 	return nil

decode_test.go

@@ -279,6 +279,25 @@ func TestDecoder(t *testing.T) {
 			"a: 50cent_of_dollar",
 			map[string]interface{}{"a": "50cent_of_dollar"},
 		},
+
+		// Nulls
+		{
+			"v:",
+			map[string]interface{}{"v": nil},
+		},
+		{
+			"v: ~",
+			map[string]interface{}{"v": nil},
+		},
+		{
+			"~: null key",
+			map[interface{}]string{nil: "null key"},
+		},
+		{
+			"v:",
+			map[string]*bool{"v": nil},
+		},
+
 		{
 			"v: .inf\n",
 			map[string]interface{}{"v": math.Inf(0)},

parser/parser.go

@@ -173,10 +173,16 @@ func (p *Parser) parseMappingValue(ctx *Context) (ast.Node, error) {
 	ctx.progress(1)          // progress to mapping value token
 	tk := ctx.currentToken() // get mapping value token
 	ctx.progress(1)          // progress to value token
-	value, err := p.parseToken(ctx, ctx.currentToken())
+	var value ast.Node
+	if vtk := ctx.currentToken(); vtk == nil {
+		value = ast.Null(token.New("null", "null", tk.Position))
+	} else {
+		v, err := p.parseToken(ctx, ctx.currentToken())
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to parse mapping 'value' node")
 		}
+		value = v
+	}
 	keyColumn := key.GetToken().Position.Column
 	valueColumn := value.GetToken().Position.Column
 	if keyColumn == valueColumn {
@@ -299,6 +305,9 @@ func (p *Parser) parseMapKey(tk *token.Token) ast.Node {
 	if tk.Type == token.MergeKeyType {
 		return ast.MergeKey(tk)
 	}
+	if tk.Type == token.NullType {
+		return ast.Null(tk)
+	}
 	return nil
 }
 

scanner/context.go

@@ -66,6 +66,10 @@ func (c *Context) isEOS() bool {
 	return len(c.src)-1 <= c.idx
 }
 
+func (c *Context) isNextEOS() bool {
+	return len(c.src)-1 <= c.idx+1
+}
+
 func (c *Context) next() bool {
 	return c.idx < c.size
 }

scanner/scanner.go

@@ -364,7 +364,7 @@ func (s *Scanner) scan(ctx *Context) (pos int) {
 			return
 		case ':':
 			nc := ctx.nextChar()
-			if nc == ' ' || nc == '\n' {
+			if nc == ' ' || nc == '\n' || ctx.isNextEOS() {
 				// mapping value
 				tk := s.bufferedToken(ctx)
 				if tk != nil {

token/token.go

@@ -274,6 +274,8 @@ type ReservedKeyword string
 const (
 	// Null `null` keyword
 	Null ReservedKeyword = "null"
+	// NullSymbol `~` keyword
+	NullSymbol = "~"
 	// False `false` keyword
 	False = "false"
 	// True `true` keyword
@@ -299,6 +301,16 @@ var (
 				Position:      pos,
 			}
 		},
+		NullSymbol: func(value, org string, pos *Position) *Token {
+			return &Token{
+				Type:          NullType,
+				CharacterType: CharacterTypeMiscellaneous,
+				Indicator:     NotIndicator,
+				Value:         value,
+				Origin:        org,
+				Position:      pos,
+			}
+		},
 		False: func(value string, org string, pos *Position) *Token {
 			return &Token{
 				Type:          BoolType,