ZeroDivisionError in evaluate.py

This is the error I get when trying to run xqrs detection algorithm from Google Colab as well locally.
I have used demo.ipynb from the repo itself.

/usr/local/lib/python3.6/dist-packages/wfdb/processing/evaluate.py in _calc_stats(self)
118 # No tn attribute
119
--> 120 self.sensitivity = float(self.tp) / float(self.tp + self.fn)
121 self.positive_predictivity = float(self.tp) / self.n_test
122

ZeroDivisionError: float division by zero

The error seems very weird in the sense that even when I comment the particular line, the error still shows in the same line.

まず demo.ipynb の traceback を再現し、次に sensitivity と positive_predictivity の計算周辺にある evaluate.py の _calc_stats を調べます。どの入力で分母がゼロになるかを確認し、適切な回帰チェックでその挙動をカバーしたうえで、この ZeroDivisionError なしに XQRS の例を実行できることを完了条件とします。