If this were Scala, `_extract_concise_traceback` would probably have a return type of `Option[(String, String, Int)]` and use `None` to signal errors.  I think it would be cleaner to return `None` here and change this check to `if tb is not None`.  Then, the error message "Error, could not extract traceback info" could go here in _JavaStackTrace.  This is consistent with the other changes here that moved more of the string formatting out of `_extract_concise_traceback`.