Custom Icon not Showing up in Diagrams as Code

I'm trying to use a Custom Node Type in this python diagrams as code library (website/docs] & pypi link). Below is (a minimal reproduceable example snippet of) my code:

from diagrams import Diagram
from diagrams import Edge
from diagrams.custom import Custom
from diagrams.gcp.devtools import ContainerRegistry
from diagrams.gcp.ml import AIPlatform

with Diagram(name="my_diagram",
    filename="diagrams/my_diagram_rec",
    show=True,
):

    # nodes
    vertexai = AIPlatform("Vertex AI")
    gcr = ContainerRegistry("Container Registry")
    gitlab_repo = Custom("Git Repo", "./diagrams/resources/gitlablogo.png")

    # diagram structure includind Edge attributes
    gitlab_repo >> Edge(label="Code \nConfig.yml \nEnvironment.yml") >> gcr
    gcr >> Edge(label="Docker Image") >> vertexai
    vertexai >> Edge(label="launches \nspecified \nmachine-size")

And confirmation that the gitlablogo.png file exists at the location I reference it at:

 ~/my-repo  issue49-diagrams $  ls diagrams/resources                ok py  17:24:23
gitlablogo.png

But when I run python diagrams/so_q_diagram.py, the image that pops up doesn't show my custom icon (the gitlab logo):

ok this was annoying and feels like a bug but apparently including a filename param in the with Diagram(... statement causes the custom icon to disappear. Because, without changing the location of gitlablogo.png, running the exact code above with one single change --commenting out filename="diagrams/my_diagram_rec",-- now causes the diagram image to render as expected: