Apoc.import.graphml doesn't work for edges

[rohankharwar]

Problem Statement

I am trying to export some data using the apoc.export.csv.data and then import using apoc.import.graphml.
When I run apoc.export.csv.data for extracting both nodes and rels in a single file and then import that single file using apoc.import.graphml, it works fine.

But for performance and parallelize it I am trying to run for nodes and rels separately.
So we get 2 files - one for nodes and other for relationships.
Then import each the nodes file first and then the relationship file.
However the problem is apoc.import.graphml works fine for the nodes but then fails for rels giving error as java null pointer exception.
The Relationship file does have the source and target node ids so it should be able to load the data.

I can easily reproduce this using the following queries.

Reproducible steps

//Extract node files
MATCH (person:Person)-[actedIn:ACTED_IN]->(movie:Movie)
WHERE person.name starts with "K"
with collect(person)+collect(movie) as node
CALL apoc.export.graphml.data(node, [], "/Users/rohankharwar/Downloads/movies_nodes.graphml", {stream: false})
YIELD file, nodes, relationships, properties, data
RETURN file, nodes, relationships, properties, data;

//Extract Relationship files
MATCH (person:Person)-[actedIn:ACTED_IN]->(movie:Movie)
WHERE person.name starts with "K"
with collect(person)+collect(movie) as node, collect(actedIn) as rels
CALL apoc.export.graphml.data([], rels, "/Users/rohankharwar/Downloads/movies_rels.graphml", {stream: false})
YIELD file, nodes, relationships, properties, data
RETURN file, nodes, relationships, properties, data;

//graphml file import nodes
CALL apoc.import.graphml("file:///Users/rohankharwar/Downloads/movies_nodes.graphml", {readLabels:true})

//graphml file import rels
CALL apoc.import.graphml("file:///Users/rohankharwar/Downloads/movies_rels.graphml", {readLabels:true})

We get the following error (attached image)

Simple Dataset (where it's possibile)

I just used the movies dataset.

Versions

• OS: Linux
• Neo4j: 4.3.10 , 4.4.4
• Neo4j-Apoc: 4.3.0.5, 4.4.0.3

[robobenklein]

I can confirm this problem only occurs when readLabels is true:

When it is false the ratio of edges to nodes is about 1.0:

When set to true, it ends up missing almost half the edges:

My dataset is a DAG, with every node having exactly one parent edge, so it's easy to tell that the graph is broken when imported with readLabels.