List slicing may return a concrete sublist on Apache AGE when either the slice start bound or end bound is `null`.

[Silence6666668]

Describe the bug
List slicing may return a concrete sublist on Apache AGE when either the slice start bound or end bound is null.

For example, in the minimized repro below, [1,2,3][1..null] should evaluate to null under Cypher null-propagation semantics. Instead, AGE treats the null bound like an omitted bound and returns [2, 3].

The same issue appears symmetrically for a null start bound.

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?

SELECT create_graph('expr_slice_bug');

No graph data is required beyond creating an empty 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: expr_slice_bug
• No extra extensions or special configuration were required

What is the command that caused the error?

SELECT * FROM cypher('expr_slice_bug', $$
  RETURN [1, 2, 3][1..null] AS v
$$) AS (v agtype);

Returned result on AGE:

[2, 3]

Expected behavior
The query should return:

null

Both Neo4j and Memgraph return null for the equivalent Cypher query.

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 symmetric variant with a null start bound shows the same issue:

SELECT * FROM cypher('expr_slice_bug', $$
  RETURN [1, 2, 3][null..2] AS v
$$) AS (v agtype);

Expected result on Neo4j and Memgraph:

null

Observed result on AGE:

[1, 2]

A normal non-null slice behaves as expected on the same AGE instance:

SELECT * FROM cypher('expr_slice_bug', $$
  RETURN [1, 2, 3][1..2] AS v
$$) AS (v agtype);

Observed result on AGE:

[2]

There is also an internal inconsistency when both bounds are null:

SELECT * FROM cypher('expr_slice_bug', $$
  RETURN [1, 2, 3][null..null] AS v
$$) AS (v agtype);

Neo4j and Memgraph both return:

null

But AGE reports:

ERROR:  slice start and/or end is required

So AGE appears to treat null slice bounds inconsistently:

• one null bound is interpreted like an omitted boundary
• two null bounds trigger an error

Neither behavior matches the null result returned by Neo4j and Memgraph.