<img src> fails assert

The following:

...raises an AssertionError because `src` exists in the element's attributes yet it's `None`.

The "problematic" source code:

if tag == "img" and start and not self.ignore_images:
if "src" in attrs:
assert attrs["src"] is not None

- html2text version: 2020.1.16
- Python version: 3.11.4