error on click in dag-dependencies - airflow 2.1

[jcmartins]

Python version: 3.7.9

Airflow version: 2.1.0

Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 2447, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1952, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1821, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python3.7/site-packages/flask/_compat.py", line 39, in reraise
raise value
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1950, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1936, in dispatch_request
return self.view_functionsrule.endpoint
File "/usr/local/lib/python3.7/site-packages/airflow/www/auth.py", line 34, in decorated
return func(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/airflow/www/decorators.py", line 97, in view_func
return f(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/airflow/www/decorators.py", line 60, in wrapper
return f(*args, **kwargs)
File "/usr/local/lib/python3.7/site-packages/airflow/www/views.py", line 4003, in list
if SerializedDagModel.get_max_last_updated_datetime() > self.last_refresh:
TypeError: '>' not supported between instances of 'NoneType' and 'datetime.datetime'

What you expected to happen:
See the dags dependencies

What do you think went wrong?
It's happen only if I don't have any dag yet.

How to reproduce it:
With any dag created click in
menu -> browser -> dag-dependencies

[boring-cyborg]

Thanks for opening your first issue here! Be sure to follow the issue template!

[jhtimmins]

@jcmartins thanks for submitting. Do you want to submit a fix as well?

[uranusjr]

This reminds me of a task I left on the backburner, so I submitted a fix to this together.