problem seems to/could be in /usr/lib/python3.8/email/base64mime.py


```
def body_encode(s, maxlinelen=76, eol=NL):
    r"""Encode a string with base64.

    Each line will be wrapped at, at most, maxlinelen characters (defaults to
    76 characters).

    Each line of encoded text will end with eol, which defaults to "\n".  Set
    this to "\r\n" if you will be using the result of this function directly
    in an email.
    """
    if not s:
        return s
```

If function is supposed to return str for any bytes input, then there it is returning the original bytes instance.. which is the trouble. it should return `""` and that's it ?
 
I would like to work/contribute on this issue.. I'll further investigate this issue and possible solution and comes with a patch rather sooner than later..