[I] List-comprehension `WHERE` filters may mishandle `null` elements. [age]

["Silence6666668 (via GitHub)" <gi...@apache.org>]

Silence6666668 opened a new issue, #2393:
URL: https://github.com/apache/age/issues/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:
   
   ```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', $$
     RETURN [x IN [null,1] WHERE x IS NULL] AS v
   $$) AS (v agtype);
   ```
   
   Returned result on AGE:
   ```text
   []
   ```
   
   **Expected behavior**
   The `WHERE x IS NULL` filter should keep the null element:
   
   ```text
   [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:
   
   ```pgsql
   SELECT * FROM cypher('fuzz_graph', $$
     RETURN [x IN [null,1,null] WHERE x IS NULL] AS v
   $$) AS (v agtype);
   ```
   
   Apache AGE returns:
   ```text
   []
   ```
   
   Expected result:
   ```text
   [null, null]
   ```
   
   Neo4j and Memgraph both return `[null, null]`.
   
   The opposite filter is also wrong on AGE:
   
   ```pgsql
   SELECT * FROM cypher('fuzz_graph', $$
     RETURN [x IN [null,1] WHERE x IS NOT NULL] AS v
   $$) AS (v agtype);
   ```
   
   Apache AGE returns:
   ```text
   [null, 1]
   ```
   
   Expected result:
   ```text
   [1]
   ```
   
   Neo4j and Memgraph both return `[1]`.
   
   For reference, the plain list comprehension without a filter behaves as expected:
   
   ```pgsql
   SELECT * FROM cypher('fuzz_graph', $$
     RETURN [x IN [null,1] | x] AS v
   $$) AS (v agtype);
   ```
   
   Apache AGE returns:
   ```text
   [null, 1]
   ```
   
   So the issue appears to be specifically in the `WHERE` filtering phase of list comprehension evaluation when `null` elements are present.
   


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Re: [I] List-comprehension `WHERE` filters may mishandle `null` elements. [age]

["gregfelice (via GitHub)" <gi...@apache.org>]

gregfelice closed issue #2393: List-comprehension `WHERE` filters may mishandle `null` elements.
URL: https://github.com/apache/age/issues/2393


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