YGY-001 opened a new issue, #2554:
URL: https://github.com/apache/age/issues/2554
**Reproduction**
```sql
LOAD 'age';
SET search_path = ag_catalog, public;
SELECT ag_catalog.create_graph('age_issue_case18');
SELECT *
FROM ag_catalog.cypher('age_issue_case18', $$
CREATE (n {id: 1})
$$) AS (v agtype);
SELECT *
FROM ag_catalog.cypher('age_issue_case18', $$
MATCH (n)
RETURN DISTINCT n AS value
UNION ALL
RETURN null AS value
$$) AS (value agtype);
```
**Expected**
The query returns the matched vertex and one `null` row. `UNION ALL` permits
both rows, and `null` is a valid value for the same result column.
**Actual**
```text
ERROR: type with OID 4026532032 does not exist
```
The numeric OID varies with the fresh database. It is generated internally;
there is no OID or type name in the Cypher input. The failure reproduces on a
fresh AGE 1.8.0 / PostgreSQL 18.6 graph.
**Controls**
The following queries succeed on the same graph:
```cypher
MATCH (n)
RETURN n AS value
UNION ALL
RETURN null AS value
```
```cypher
RETURN 1 AS value
UNION ALL
RETURN null AS value
```
The failure therefore requires the entity branch's `RETURN DISTINCT` path;
it is not a user-supplied missing-type or missing-OID error. The original
audit Cases 951, 1167, and 1888 are deduplicated under this one family. Case
1167 uses `UNION ALL`; Cases 951 and 1888 use the default `UNION` spelling.
**Environment**
Apache AGE `1.8.0` on PostgreSQL `18.6`, Docker image
`apache/age:release_PG18_1.8.0`.
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