Docs: git.remote.Remote.push: length of a list won't be null

[tometzky]

https://gitpython.readthedocs.io/en/stable/reference.html?highlight=push#git.remote.Remote.push

If the operation fails completely, the length of the returned IterableList will be null.

I don't think the length of a list can be null. Either the length will be 0 or the returned value will be null.