Yes, that’s correct.
None if the if the character indices don’t map to a valid span. I’ve just updated this in the documentation to make it more clear. Thanks!
In the future, I think a better place for reporting spaCy-only problems like this one is the spaCy issue tracker or for usage questions, StackOverflow. This way, more people will see it and if something is a bug, it’ll make it easier for us to track the changes on GitHub.