apoc vRelationships with null values throw nullPointerExceptions in BoltEntityAdapter

[quot-zz]

Creating a virtual relationship using apoc.create.vRelationship can result in objects being returned from neo4j containing null values where the properties wouldn't be passed in a normal relationship. An example of this is if a property of the virtual relationship is being mapped from a node property that is null. Trying to retrieve these virtual relationships results in a null pointer exception being thrown.

Expected Behavior

Virtual relationship properties that are returned as null from an apoc.create.vRelationship call should be mapped to null

Current Behavior

Properties containing null values are mapped as objects of type NullValue and get transformed to null when the value.asObject() method is called in the toMapped method in BoltEntityAdapter - https://github.com/neo4j/neo4j-ogm/blob/master/bolt-driver/src/main/java/org/neo4j/ogm/drivers/bolt/driver/BoltEntityAdapter.java#L121
On the subsequent line object.getClass() is called, resulting in a null pointer exception - https://github.com/neo4j/neo4j-ogm/blob/master/bolt-driver/src/main/java/org/neo4j/ogm/drivers/bolt/driver/BoltEntityAdapter.java#L122
A simple null check on object after Object object = value.asObject() should solve this problem.

Context

My current use case is trying to create virtual relationships to model data structures that require the use of intermediate nodes. For example I want to model the relationship (A)-[:r]->(B) except r also needs to reference (C). So in Neo4J I have modelled it as follows:
(A)-[:r1]->(R)-[:r2]-(B) and (R)-[:r3]->(C)

I don't want this complexity to be returned to the client so I create the virtual relationship as mentioned above, except if I am mapping properties from C to r and C does not exist they get mapped as null. This would be fine except for the null pointer exception issues mentioned.

Your Environment

• Java version:
• Neo4j version: 4.4.5
• OGM Version: 3.2.35
• OGM Transport used: Bolt
• Neo4j Java Driver version (in case of Bolt transport): 4.3.6

Steps to Reproduce

Node

@NodeEntity
public class TestNode {

}

Relationship

@RelationshipEntity(type = "test_relationship")
public class TestRelationship {
    @StartNode
    TestNode startNode;
    @EndNode
    TestNode endNode;
    private String testField;
}

Repository

@Repository
public interface TestRelationshipRepository extends PagingAndSortingRepository<TestRelationship, String> {

    @Query("MATCH (n:TestNode) return apoc.create.vRelationship(n, 'test_relationship', {testField:null}, n)")
    Optional<TestRelationship> getRelationship();
}

[michael-simons]

Thanks for the report and the good analysis. The fix will be released shortly.