Graph view crashes when a DAG is empty

[uranusjr]

Apache Airflow version

main (development)

If "Other Airflow 2 version" selected, which one?

No response

What happened?

When an empty DAG is created without any tasks, the DAG can be parsed and triggered in the UI, but the UI crashes when you click on Graph. The entire screen (except the top bar) disappears.

Uncaught TypeError: u.nodes.children[0] is undefined
    gQ http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    wa http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    Ms http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    wl http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    vu http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    mu http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    gu http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    iu http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    ru http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    _ http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
    O http://localhost:28080/static/dist/grid.abc695e791ed71742eea.js:2
grid.abc695e791ed71742eea.js:2:2750893

What you think should happen instead?

The UI should load correctly. The graph should be empty (no blocks), but other controls should still load.

How to reproduce

1. Load this DAG into Airflow

   from airflow.decorators import dag
   
   @dag(schedule=None)
   def empty():
       pass
   
   empty()

2. Trigger a run from the Home page.

3. Click into the DAG detail view

4. Clikc on Graph

Operating System

n/a

Versions of Apache Airflow Providers

No response

Deployment

Other

Deployment details

No response

Anything else?

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[josix]

I made this change to let the page not become blank, but is it okay to display empty dag like this?

[romsharon98]

I made this change to let the page not become blank, but is it okay to display empty dag like this?

Yes, I think this is how it should look.

[uranusjr]

Agreed, I think an empty page is good enough. An empty DAG is a user error anyway, and it’s probably good enough we don’t crash.