AttributeError: 'NoneType' object has no attribute 'modified'

[Relebohile3369]

Hi,

I need help, I'm encountering this error below when I run my app on localhost:5000. Can you please help me to fix this error?

"
File "/Users/lesmacbookpro/Desktop/Xero/THE RIGHT ONE/xero-python-oauth2-starter-master/venv/lib/python3.11/site-packages/flask_session/sessions.py", line 343, in save_session
if session.modified:
^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'modified'
127.0.0.1 - - [19/Aug/2023 18:12:19] "GET / HTTP/1.1" 500 -"

[SherryFeng123]

What worked for me was installing an older version of flask. The version I did was flask==2.2.5

[CedricConday]

This isn't actually a xero-python issue — the traceback is in flask_session/sessions.py, so it's a Flask / Flask-Session version mismatch. if session.modified fails because open_session() returned None, which happens when your installed Flask-Session doesn't support your installed Flask (Flask 2.3 removed internals that older Flask-Session releases relied on).

Two clean fixes:

• Upgrade Flask-Session to a modern release: pip install -U Flask-Session (0.5.0+ restored compatibility with current Flask) — preferred, keeps you up to date.
• Or pin Flask below the break, which is what @SherryFeng123's flask==2.2.5 effectively does.

Pinning Flask down works but leaves you on an old Flask; upgrading Flask-Session is the better long-term fix. After switching, clear your session backend (e.g. delete the flask_session/ cache dir) so a stale null session isn't reused.