fix implicit null value before collect entry

Author: goccy

decode_test.go

@@ -977,6 +977,10 @@ func TestDecoder(t *testing.T) {
 		{
 			"{}", struct{}{},
 		},
+		{
+			"{a: , b: c}",
+			map[string]any{"a": nil, "b": "c"},
+		},
 		{
 			"v: /a/{b}",
 			map[string]string{"v": "/a/{b}"},

parser/parser.go

@@ -154,6 +154,9 @@ func (p *parser) createMapValueNode(ctx *context, key ast.MapKeyNode, colonToken
 		nullToken := p.createNullToken(colonToken)
 		ctx.insertToken(ctx.idx, nullToken)
 		return ast.Null(nullToken), nil
+	} else if tk.Type == token.CollectEntryType {
+		// implicit null value.
+		return ast.Null(tk), nil
 	}
 	var comment *ast.CommentGroupNode
 	if tk.Type == token.CommentType {

parser/parser_test.go

@@ -87,6 +87,7 @@ func TestParser(t *testing.T) {
 		"a_ok: \r  bc: 2\r",
 		"a_mk: \n  bd: 3\n",
 		"a: :a",
+		"{a: , b: c}",
 	}
 	for _, src := range sources {
 		if _, err := parser.Parse(lexer.Tokenize(src), 0); err != nil {