Consider the test cases below. It is unexpected that the following queries all return 1, since `NULL IS NOT NULL` and `NULL IS NULL` could not be evaluated to `true` at the same time.

```sql
CREATE TABLE t0(c0 INT);
CREATE TABLE t1(c1 INT);
INSERT INTO t1 (c1) VALUES (1);
SELECT * FROM t0 RIGHT JOIN t1 ON 1; -- NULL 1

-- At least one of the query should return empty result
SELECT * FROM t0 RIGHT JOIN t1 ON 1 WHERE (NULL IS NOT NULL); -- NULL 1
SELECT * FROM t0 RIGHT JOIN t1 ON 1 WHERE (NULL IS NULL); -- NULL 1
```

Here's the version I used:
```
docker run -i -t pkleef/virtuoso-opensource-7 version

[pkleef/virtuoso-opensource-7:7.2.12-r17.1-g466615d-ubuntu]

This Docker image is using the following version of Virtuoso:

Virtuoso Open Source Edition (Column Store) (multi threaded)
Version 7.2.12-dev.3238-pthreads as of Dec 15 2023 (e49c0644f)
Compiled for Linux (x86_64-ubuntu_bionic-linux-gnu)
Copyright (C) 1998-2023 OpenLink Software
```
Unexpected results when Using `RIGHT JOIN`
This is a GitHub Issue
repo:virtuoso-opensource
owner:openlink
Title : Unexpected results when Using `RIGHT JOIN`
Issue date:

--- start body ---
Consider the test cases below. It is unexpected that the following queries all return 1, since `NULL IS NOT NULL` and `NULL IS NULL` could not be evaluated to `true` at the same time.

```sql
CREATE TABLE t0(c0 INT);
CREATE TABLE t1(c1 INT);
INSERT INTO t1 (c1) VALUES (1);
SELECT * FROM t0 RIGHT JOIN t1 ON 1; -- NULL 1

-- At least one of the query should return empty result
SELECT * FROM t0 RIGHT JOIN t1 ON 1 WHERE (NULL IS NOT NULL); -- NULL 1
SELECT * FROM t0 RIGHT JOIN t1 ON 1 WHERE (NULL IS NULL); -- NULL 1
```

Here's the version I used:
```
docker run -i -t pkleef/virtuoso-opensource-7 version

[pkleef/virtuoso-opensource-7:7.2.12-r17.1-g466615d-ubuntu]

This Docker image is using the following version of Virtuoso:

Virtuoso Open Source Edition (Column Store) (multi threaded)
Version 7.2.12-dev.3238-pthreads as of Dec 15 2023 (e49c0644f)
Compiled for Linux (x86_64-ubuntu_bionic-linux-gnu)
Copyright (C) 1998-2023 OpenLink Software
```
--- end body ---
