Potential bug computing len of argspec.defaults

[slothyrulez]

TypeError object of type 'NoneType' has no len()

https://docs.python.org/3.8/library/inspect.html?highlight=inspect#inspect.getfullargspec
https://docs.python.org/3.8/library/inspect.html?highlight=inspect#inspect.getargspec

defaults is an n-tuple of default argument values corresponding to the last n positional parameters, or None if there are no such defaults defined

https://github.com/unhaggle/django-memoize/blob/1ca9af73adf3e5e336aafe85b82993a0a3a66a77/memoize/__init__.py?_pjax=%23repo-content-pjax-container#L250

elif abs(i - args_len) <= len(argspec.defaults)

Possible fix:

elif abs(i - args_len) <= len(argspec.defaults if argspec.defaults else [])