Sort in subquery is lost when converting SqlNode to Relnode

// SqlToRelConverterTest
@Test public void testSortInSubquery() {
    final String sql = "select ename from (select ename from emp order by ename) a";
    sql(sql).ok();
  }

<TestCase name="testSortInSubquery">
        <Resource name="sql">
            <![CDATA[select ename from (select ename from emp order by ename) a]]>
        </Resource>
        <Resource name="plan">
            <![CDATA[
LogicalProject(ENAME=[$1])
  LogicalTableScan(table=[[CATALOG, SALES, EMP]])
]]>
        </Resource>
    </TestCase>