The header retrieval crashes the receiver

# Summary

The receiver crashes on receiving the webhook because of what seems to be an internal error upon retrieving values from HTTP headers.
This crash does not lead to server downtime, but artifact handling does not occur at all.

# Steps to reproduce

Receive a valid webhook from UCB, or just cURL the endpoint with POST.

# Environment

* Python 3.9 on the host machine
* This is different from what Docker uses, which is 3.8
* Docker Container version

# Notes

This issue needs more investigation as I installed the libraries and updated a part of them.
This could be the problem specific to Python 3.9, as my old environment of 3.8 has no issue whatsoever.
It's weird that the Docker container is running on Pypy 3.8 though...?