RelToSqlConverter handling "NOT IN" incorrectly

@Test public void testNotInOperator() {
  final RelBuilder builder = relBuilder().scan("EMP");
  final RexNode condition =
    builder.call(SqlStdOperatorTable.NOT_IN, builder.field("DEPTNO"),
      builder.literal(20), builder.literal(30));
  final RelNode root = relBuilder().scan("EMP").filter(condition).build();
  final String sql = toSql(root);
  final String expectedSql = "SELECT *\n"
    + "FROM \"scott\".\"EMP\"\n"
    + "WHERE \"DEPTNO\" NOT IN (20, 30)";
  assertThat(sql, isLinux(expectedSql));
}

Expected: is "SELECT *\nFROM \"scott\".\"EMP\"\nWHERE \"DEPTNO\" NOT IN (20, 30)"
but: was "SELECT *\nFROM \"scott\".\"EMP\"\nWHERE \"DEPTNO\" NOT IN 20 NOT IN 30"