CTFd: serve.py crashes without any errors on Windows

Environment:

• CTFd Version/Commit: https://github.com/CTFd/CTFd/commit/d23f59dbd51925aac1aa6294c934d701953075d0
• Operating System: Windows 10, python 3.9.2
• Web Browser and Version: n/a

What happened? Some errors from pybluemonday go code upon starting, see stacktrace below.

I reverted to the commit before pybluemonday was implemented https://github.com/CTFd/CTFd/commit/8de9819bd45be7483f252d37d0d0a2977dd7bd6d and it was able to start normally.

What did you expect to happen? No errors and CTFd starts normally.

How to reproduce your issue

1. Install pip dependencies pip install -r requirements.txt
2. Start with python serve.py

Any associated stack traces or error logs

PS C:\Users\Ben10\Documents\GitHub\CTFd> python serve.py
 * Importing gevent and monkey patching. Use --disable-gevent to disable.
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x0 pc=0x6d2efafd]

goroutine 17 [running, locked to thread]:
github.com/microcosm-cc/bluemonday.(*Policy).init(...)
        C:/Users/RUNNER~1/AppData/Local/Temp/tmp4rqegntm/src/github.com/microcosm-cc/bluemonday/policy.go:173
github.com/microcosm-cc/bluemonday.(*Policy).AllowElements(0x0, 0xc0002b00e0, 0x1, 0x1, 0x0)
        C:/Users/RUNNER~1/AppData/Local/Temp/tmp4rqegntm/src/github.com/microcosm-cc/bluemonday/policy.go:488 +0x2d
reflect.Value.call(0x6d361b00, 0x0, 0x1613, 0x6d36825e, 0x4, 0xc000279e40, 0x1, 0x1, 0x6d3a4240, 0xc000064f60, ...)
        C:/hostedtoolcache/windows/go/1.14.12/x64/src/reflect/value.go:460 +0x8b2
reflect.Value.Call(0x6d361b00, 0x0, 0x1613, 0xc000279e40, 0x1, 0x1, 0x0, 0x1613, 0xc000279e80)
        C:/hostedtoolcache/windows/go/1.14.12/x64/src/reflect/value.go:321 +0xbb
main.CallPolicyFunctionWithString(0xc007fcfd52, 0x1e2469cabf0, 0x1e2469cac80)
        C:/Users/RUNNER~1/AppData/Local/Temp/tmp4rqegntm/src/github.com/ColdHeat/pybluemonday/bluemonday.go:145 +0x23c
main._cgoexpwrap_8294da18a757_CallPolicyFunctionWithString(0x1e207fcfd52, 0x1e2469cabf0, 0x1e2469cac80)
        _cgo_gotypes.go:163 +0x44