Wrong missing environment variable name if using prefix

[nfantone]

If setting a prefix, the name of a missing environment variable is incorrectly reported without it.

# settings.py

env = environ.Env()
env.prefix = "DJANGO_"

SECRET_KEY = env.str("SECRET_KEY")

    raise ImproperlyConfigured(error_msg) from exc
django.core.exceptions.ImproperlyConfigured: Set the SECRET_KEY environment variable

The exception message should really read "Set the DJANGO_SECRET_KEY environment variable".

[spenserblack]

Just stumbled on this too. This isn't intentional, is it?