List-comprehension WHERE filters may mishandle null elements. #2393

Describe the bug
List-comprehension WHERE filters may mishandle null elements.

In the repro below, Apache AGE drops null elements even when the filter explicitly selects them with x IS NULL. It also fails to remove null elements when the filter is x IS NOT NULL.

Both Neo4j and Memgraph return the expected filtered lists.

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:

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?

SELECT * FROM cypher('fuzz_graph', $$
  RETURN [x IN [null,1] WHERE x IS NULL] AS v
$$) AS (v agtype);

Returned result on AGE:

[]

Expected behavior
The WHERE x IS NULL filter should keep the null element:

[null]

Neo4j returns [null], and Memgraph 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 more clearly with a second null element:

SELECT * FROM cypher('fuzz_graph', $$
  RETURN [x IN [null,1,null] WHERE x IS NULL] AS v
$$) AS (v agtype);

Apache AGE returns:

[]

Expected result:

[null, null]

Neo4j and Memgraph both return [null, null].

The opposite filter is also wrong on AGE:

SELECT * FROM cypher('fuzz_graph', $$
  RETURN [x IN [null,1] WHERE x IS NOT NULL] AS v
$$) AS (v agtype);

Apache AGE returns:

[null, 1]

Expected result:

[1]

Neo4j and Memgraph both return [1].

For reference, the plain list comprehension without a filter behaves as expected:

SELECT * FROM cypher('fuzz_graph', $$
  RETURN [x IN [null,1] | x] AS v
$$) AS (v agtype);

Apache AGE returns:

[null, 1]

So the issue appears to be specifically in the WHERE filtering phase of list comprehension evaluation when null elements are present.