mention_confidence not available for some namespace type

[wonjininfo]

I found that the "mention_confidence" entry does not exist for the namespace "TransformersModelForTokenClassificationNerStep".
While I think this is reasonable and might be intentional, I wanted to make a note about this observation.

To maintain consistency, perhaps imputing "mention_confidence" with something like "n/a" (or "Prob:TBA") could be an option. What do you think?