NVL and COALESCE does not work on RIGHT JOIN

When using NVL or COALESCE in a SQL query involving a NULL value from the right-side table, the function returns null instead of the expected value.

### Affected Version

Druid 33.0.0

### Description

Using this sample query:
```
SELECT ds1.Key, COALESCE(ds1.LastUsed, 'N/A'), COALESCE(ds2.LastUsed, 'N/A')
FROM (
SELECT Key, MAX(__time) AS LastUsed
FROM datasource1
WHERE __time >= CURRENT_TIMESTAMP - INTERVAL 90 DAY
GROUP BY 1
) ds1
FULL OUTER JOIN (
SELECT Key, MAX(__time) AS LastUsed
FROM datasource2
WHERE __time >= CURRENT_TIMESTAMP - INTERVAL 90 DAY
GROUP BY 1
) ds2 ON ds1.Key = ds2.Key
ORDER BY 1, COALESCE(ds2.LastUsed, ds1.LastUsed) DESC
```

Given data like:
```
datasource1

__time | Key
--------------------+----
2025-09-22T01:00:00 | 1
2025-09-22T02:00:00 | 2

datasource2

__time | Key
--------------------+----
2025-09-22T11:00:00 | 1
2025-09-22T13:00:00 | 3
```

Expected Result would be:
```
Key | EXPR$1 | EXPR$2
----+---------------------+--------------------
1 | 2025-09-22T01:00:00 | 2025-09-22T11:00:00
2 | 2025-09-22T02:00:00 | N/A
3 | N/A | 2025-09-22T13:00:00
```

Actual Result is:
```
Key | EXPR$1 | EXPR$2
----+---------------------+--------------------
1 | 2025-09-22T01:00:00 | 2025-09-22T11:00:00
2 | 2025-09-22T02:00:00 | null
3 | N/A | 2025-09-22T13:00:00
```

The same holds true for NVL. For example: `SELECT ds1.Key, NVL(ds1.LastUsed, CURRENT_TIMESTAMP), NVL(ds2.LastUsed, CURRENT_TIMESTAMP)` returns a null entry in EXPR$2

Start by reproducing the sample FULL OUTER JOIN query on Druid 33.0.0 and compare COALESCE and NVL results for NULL values from the right-side table. Trace the join and expression handling that produces the null result; done when both functions return their fallback values for the missing right-side row.

Written by the indexing model from the issue text.