Silence6666668 opened a new issue, #2394:
URL: https://github.com/apache/age/issues/2394
**Describe the bug**
List-comprehension projection over a `null` element may produce a nested
list instead of `null`.
In the repro below, Apache AGE evaluates:
```cypher
[x IN [null] | x + 1]
```
as:
```text
[[null, 1]]
```
Instead of:
```text
[null]
```
This also affects mixed lists such as `[1, null, 2]`, where the null element
becomes `[null, 1]` instead of staying `null`.
**How are you accessing AGE (Command line, driver, etc.)?**
- PostgreSQL `cypher(...)` wrapper through the local Python
differential-testing harness
- Reproducible directly in `psql` inside the Docker container
**What data setup do we need to do?**
No graph data is required beyond creating an empty graph:
```pgsql
SELECT create_graph('fuzz_graph');
```
**What is the necessary configuration info needed?**
- Plain Apache AGE Docker image was enough
- Docker image in local repro: `apache/age`
- AGE extension version: `1.7.0`
- PostgreSQL version: `18.1`
- Graph name used in repro: `fuzz_graph`
- No extra extensions or special configuration were required
**What is the command that caused the error?**
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
RETURN [x IN [null] | x + 1] AS v
$$) AS (v agtype);
```
Returned result on AGE:
```text
[[null, 1]]
```
**Expected behavior**
The null element should stay null under the arithmetic projection, so the
expected result is:
```text
[null]
```
Neo4j returns `[null]`, and Memgraph also returns `[null]`.
**Environment (please complete the following information):**
- Version: Apache AGE `1.7.0`
- PostgreSQL: `18.1`
- Host OS: Windows
- Architecture: x86_64
- Deployment: Docker
**Additional context**
The same issue appears in a mixed list:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
RETURN [x IN [1,null,2] | x + 1] AS v
$$) AS (v agtype);
```
Apache AGE returns:
```text
[2, [null, 1], 3]
```
Expected result:
```text
[2, null, 3]
```
Neo4j and Memgraph both return `[2, null, 3]`.
Two nearby control cases behave correctly on the same AGE instance:
1. The same list comprehension without arithmetic projection:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
RETURN [x IN [1,null,2] | x] AS v
$$) AS (v agtype);
```
Observed result:
```text
[1, null, 2]
```
2. The arithmetic projection on a list without null elements:
```pgsql
SELECT * FROM cypher('fuzz_graph', $$
RETURN [x IN [1,2] | x + 1] AS v
$$) AS (v agtype);
```
Observed result:
```text
[2, 3]
```
So the issue appears specifically when the list-comprehension projection
expression operates on a `null` element.
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