Django webpack_loader: `Regex` Undefined?

Question

I've updated a Django app to Python 3.9 and Django 4.0, and I'm getting an error on launch:

TypeError: expected string or bytes-like object

I tracked it down to this function in python3.9/site-packages/webpack_loader/loader.py:

def filter_chunks(self, chunks):
    filtered_chunks = []

    for chunk in chunks:
        ignore = any(regex.match(chunk)
                     for regex in self.config['ignores'])
        if not ignore:
            filtered_chunks.append(chunk)

    return filtered_chunks

On the line ignore = any(regex.match(chunk)..., regex is undefined.

I ran brew upgrade python, but Homebrew said:

Warning: python 3.9.13_1 already installed

What am I missing?