UDF without parameters cannot be validated when use default conformance

public static void main(String[] args) throws Exception {
        Schema schema = new AbstractSchema() {
            @Override
            protected Map<String, Table> getTableMap() {
                return Map.of();
            }
        };
        Properties info = new Properties();
        info.setProperty(CalciteConnectionProperty.DEFAULT_NULL_COLLATION.camelName(), NullCollation.LAST.name());
        info.setProperty(CalciteConnectionProperty.CASE_SENSITIVE.camelName(), "false");
        Connection connection = DriverManager.getConnection("jdbc:calcite:", info);
        CalciteConnection calciteConnection = connection.unwrap(CalciteConnection.class);
        SchemaPlus rootSchema = calciteConnection.getRootSchema();
        rootSchema.add("test", schema);
        rootSchema.add("TEST_FUNC", ScalarFunctionImpl.create(Main.class, "testFunc"));

        Statement stat = connection.createStatement();
        ResultSet resultSet = stat.executeQuery("select test_func()");

        resultSet.next();
        String res = resultSet.getString(1);
        System.out.println(res);

    }

    public static String testFunc() {
        return "testFunc";
    }