"No POST data" in error report

Checklist

• Raised initially as discussion #7899
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.

Description

I'm using Django 3.1.7 & DRF 3.12.2. When an exception occurs in a ViewSet, Django automatically sends an email to the administrator.

The problem is that the POST data is always empty in this email:

POST: No POST data

Instead, I expect to see the JSON payload that was sent in the request body.

I added a breakpoint in django.utils.log.AdminEmailHandler.emit(), and I can confirm that request.POST is empty. But on the other hand, I'm sure that request.data was not empty in the ViewSet.

I verified that the request's Content-Type and X-Requested-With are correctly set. The only non-standard middlewares I use are corsheaders and admin_reorder; I don't think they are related to this problem.