Traceback (most recent call last):
  File "/usr/bin/gtimelog", line 1160, in on_last_month_report_activate
    window = self.monthly_window(day=day)
  File "/usr/bin/gtimelog", line 1142, in monthly_window
    first.replace(month=(day.month + 1) % 12) -
ValueError: month must be in 1..12