Hi! I discovered that FalkorDB could return non-existent relations in the OPTIONAL MATCH clause. Steps to reproduce are as follows.

1. Use the following queries to initialize the data:

CREATE (n0 :L1:L0{id : 0})
CREATE (n0 :L1{id : 4})
CREATE (n0 :L0:L1{id : 5})
CREATE (n0 :L0{id : 6})
MATCH (n0 {id : 4}), (n1 {id : 5}) MERGE(n0)-[r :T4{id : 13}]->(n1)
MATCH (n0 {id : 6}), (n1 {id : 0}) MERGE(n0)-[r :T7{id : 18}]->(n1)
MATCH (n0 {id : 0}), (n1 {id : 5}) MERGE(n0)-[r :T1{id : 22}]->(n1)

2. Please note that there is only one relation between id=4 node and id=5 node, and the relation id is 13. However, when executing the following query:

MATCH (n0)-[r0]->(n1) WHERE n0.id = 4 and n1.id = 5 OPTIONAL MATCH (n0 {id:4})-[r9]->(n1 {id:5}), (n2)-[r10]->(n3)-[r11]->(n4) RETURN n0.id, n1.id, r9.id

The result is [[4, 5, 18]], meaning that it outputs a non-existent relation id=18 between the two nodes. Adjusting the query, the database could output different non-existent relations.
Thank you!