Error "has no attribute '_base_name'" for UDT

[IlyaEp]

Hello,
First of all, I want to thank you for pygraphblas.
I have a question. To ask the question I will reproduce the sequence of actions.

1. I installed the latest version of pygraphblas via pip
2. After that I tried to run your example for user-defined types in tests. For this I had to add the following imports

from pygraphblas.types import Type, binop
from pygraphblas import lib

3. After that I ran the example. But I got an error

File "/home/ilya/.local/lib/python3.8/site-packages/pygraphblas/types.py", line 437, in __set_name__
    if cls._base_name == "UDT":
AttributeError: type object 'BF' has no attribute '_base_name'

4. To fix this error, I had to add _base_name = "UDT" attribute to the class BF

After that the error disappeared. Can you please tell me this is how it should be done or the problem is something else.
I'm also interested in #65 too.