Graph visualisation out of Python not working

General Newbie Questions
1

Hi, I'm trying to display a graph using Python and I follow the instruction on Manipulate query results - Neo4j Python Driver Manual for that. I'm using my own database, and an easy query, that in neo4j returns a small subgraph with 5 nodes and 4 relationships.
Unfortunately, python shows nothing. As far as I can see, the graph object (result_transformer_=neo4j.Result.graph) doesn't get the relationships because I can print all results for the nodes, like

for node in graph_result.nodes:
    print(node.labels)
    print(node.element_id)
    print(node[nodes_text_properties[list(node.labels)[0]]])

but doing the same with the relationships doesn't return anything (also no error message):
for relationship in graph_result.relationships:

   print("s")
    print(relationship.start_node.element_id)

Is there a bug or am I doing something wrong?

This is the whole code (without settings):

def main():
    # Verbindung mit der Graph-DB herstellen
    with GraphDatabase.driver(URI, auth=AUTH) as driver:
        driver.verify_connectivity()

    # Query to get a graphy result
    graph_result = driver.execute_query("""
       MATCH (p:person) --> (m:mail)
       WHERE p.email starts with 'pallen'
       RETURN p,m
       """,
       result_transformer_=neo4j.Result.graph,
        )

    # Draw graph
    nodes_text_properties = {  # what property to use as text for each node
        "person": "contact_name",
        "mail": "id",
    }
    visualize_result(graph_result, nodes_text_properties)


def visualize_result(query_graph, nodes_text_properties):
    visual_graph = pyvis.network.Network()

    for node in query_graph.nodes:
        node_label = list(node.labels)[0]
        node_text = node[nodes_text_properties[node_label]]
        visual_graph.add_node(node.element_id, node_text, group=node_label)

    for relationship in query_graph.relationships:
        visual_graph.add_edge(
            relationship.start_node.element_id,
            relationship.end_node.element_id,
            title=relationship.type
        )

    visual_graph.show('network.html', notebook=False)

if __name__ == "__main__":
    main()